ESD protection device and method for manufacturing the same

ABSTRACT

An ESD protection device is manufactured such that its ESD characteristics are easily adjusted and stabilized. The ESD protection device includes an insulating substrate, a cavity provided in the insulating substrate, at least one pair of discharge electrodes each including a portion exposed in the cavity, the exposed portions being arranged to face each other, and external electrodes provided on a surface of the insulating substrate and connected to the at least one pair of discharge electrodes. A particulate supporting electrode material having conductivity is dispersed between the exposed portions of the at least one pair of discharge electrodes in the cavity.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electrostatic discharge (ESD)protection device and a method for manufacturing the ESD protectiondevice, and particularly to an ESD protection device having improved ESDcharacteristics, such as discharge starting voltage, and reliability inwhich discharge electrodes are disposed in a cavity of an insulatingsubstrate so as to face each other.

2. Description of the Related Art

ESD is a phenomenon in which strong discharge is generated when acharged conductive body (e.g., human body) comes into contact with orcomes sufficiently close to another conductive body (e.g., electronicdevice). ESD causes damage or malfunctioning of electronic devices. Toprevent this, an excessively high voltage generated during dischargemust be prevented from being applied to circuits of the electronicdevices. ESD protection devices, which are also called surge absorbers,are used for such an application.

An ESD protection device is disposed, for instance, between a signalline and a ground of a circuit. The ESD protection device includes apair of discharge electrodes facing each other with a space providedtherebetween. Therefore, the ESD protection device has high resistanceunder normal operation and a signal is not sent to the ground. Anexcessively high voltage, for example, generated by static electricitythrough an antenna of a cellular phone causes discharge between thedischarge electrodes of the ESD protection device, which leads thestatic electricity to the ground. Thus, a voltage generated by staticelectricity is not applied to the circuits disposed downstream from theESD protection device, which protects the circuits.

For example, an ESD protection device shown in an exploded perspectiveview of FIG. 37 and a sectional view of FIG. 38 includes a cavity 5provided in a ceramic multilayer substrate 7 including a plurality oflaminated insulating ceramic sheets 2. Discharge electrodes 6 facingeach other and electrically connected to external electrodes 1 aredisposed in the cavity 5 that includes a discharge gas. When a breakdownvoltage is applied between the discharge electrodes 6, discharge isgenerated between the discharge electrodes 6 in the cavity 5, whichleads an excessive voltage to the ground. Consequently, the circuitsdisposed downstream from the ESD protection device are protected (see,for example, Japanese Unexamined Patent Application Publication No.2001-43954).

However, in such an ESD protection device, the discharge responsivity toESD varies significantly due to the variation in the distance betweenthe discharge electrodes. Furthermore, although the responsivity to ESDneeds to be adjusted using an area of the region sandwiched betweendischarge electrodes facing each other, the amount of adjustment islimited by the size of the product or other factors. Therefore, it maybe difficult to achieve a desired responsivity to ESD.

Furthermore, a discharge phenomenon is efficiently caused by employing astructure in which a conductive material is dispersed between dischargeelectrodes. However, with such a structure, since the conductivematerial is scattered due to an impact caused during discharge and thusthe distribution density is decreased, the discharge voltage isgradually increased each time discharge is performed. Consequently,discharge characteristics are degraded after repetitive discharges.

Moreover, such an ESD protection device poses the following problems.

Firstly, a discharge starting voltage is primarily set by adjusting thedistance between discharge electrodes. However, the distance betweendischarge electrodes is varied because of variations that occur duringproduction and a difference in shrinkage behavior between a ceramicmultilayer substrate and discharge electrodes during firing.Consequently, the discharge starting voltage of an ESD protection devicevaries. Therefore, the discharge starting voltage cannot be set withhigh precision.

Secondly, discharge electrodes in a cavity may be detached from aceramic multilayer substrate because of a decrease in the hermeticity ofthe cavity or a difference in a coefficient of thermal expansion (may bereferred to as “thermal expansivity”) between a base layer of theceramic multilayer substrate and the discharge electrodes. In such acase, the device becomes unusable as an ESD protection device, or thedischarge starting voltage is changed and, thus, the reliability of theESD protection device is degraded.

SUMMARY OF THE INVENTION

To overcome the problems described above, preferred embodiments of thepresent invention provide an ESD protection device having ESDcharacteristics that are easily adjusted and stabilized, whose dischargecharacteristics are not degraded even after repetitive discharges, andwhose discharge starting voltage can be set with high precision and amethod for manufacturing the ESD protection device.

An ESD protection device according to a preferred embodiment of thepresent invention preferably includes an insulating substrate, a cavityprovided in the insulating substrate, at least a pair of dischargeelectrodes each including a portion exposed in the cavity, the exposedportions being arranged to face each other, and external electrodesprovided on a surface of the insulating substrate and connected to thedischarge electrodes. A particulate supporting electrode material havingconductivity is preferably dispersed between the exposed portions of thedischarge electrodes in the cavity.

In the above-described structure, since a supporting electrode materialhaving conductivity is dispersed between the exposed portions of thedischarge electrodes arranged to face each other, electrons easily movein the cavity and, thus, a discharge phenomenon can be more efficientlyproduced. Thus, fluctuations in responsivity to ESD caused by variationin the distance between discharge electrodes are reduced.

Furthermore, by adjusting the amount and particle size of the supportingelectrode material dispersed in the cavity, desired ESD characteristics(e.g., discharge starting voltage) can be easily achieved.

Therefore, the ESD characteristics can be easily adjusted andstabilized.

The supporting electrode material is preferably coated with aninsulating material.

In this case, since the supporting electrode material is coated with aninsulating material, short circuits between the discharge electrodescaused by contact between adjacent particles of the supporting electrodematerial are effectively prevented.

In the cavity, creeping discharge is easily generated along a creepagesurface between an insulator and a space. By coating the supportingelectrode material with an insulating material, more creepage surfacesare provided in the cavity, which further improves the responsivity toESD.

Furthermore, by decreasing the size of a gap between particles of thesupporting electrode material coated with the insulating material, aloss caused by gaseous discharge is reduced and, thus, the degradationof discharge characteristics is prevented.

An insulating material is preferably dispersed in the cavity.

In this case, contact between particles of the supporting electrodematerial is prevented by the insulating material dispersed in thecavity. Thus, short circuits between discharge electrodes caused by thecontact between adjacent particles of the supporting electrode materialare prevented.

The insulating substrate is preferably a ceramic substrate.

In this case, the ESD protection device can be easily manufactured.

The ceramic substrate preferably includes a glass component. A sealingmember arranged to prevent the glass component in the ceramic substratefrom entering the cavity is preferably disposed between the ceramicsubstrate and the cavity.

In this case, since the sealing member prevents the glass component inthe ceramic substrate from entering the cavity, the necking of thesupporting electrode material in the cavity caused by the glasscomponent that has entered the cavity is prevented.

The degradation of an insulating property between the dischargeelectrodes caused when the glass component that has entered the cavityerodes the insulating material which coats the supporting electrodematerial or the insulating material dispersed between particles of thesupporting electrode material is also prevented.

According to another preferred embodiment of the present invention,preferably, the supporting electrode material is a conductive materialdispersed between the discharge electrodes in the cavity, and theconductive material is in contact with a bottom surface and a topsurface that define the cavity.

In the above-described configuration, when a voltage equal to or greaterthan a certain voltage is applied between the external electrodes,discharge is generated between the exposed portions of the dischargeelectrodes that face each other. This discharge is primarily creepingdischarge generated along the interface between a space of the cavityand the insulating substrate. Since the conductive material disposed ina dispersed manner is in contact with the interface along which thecreeping discharge is generated, that is, the top surface and the bottomsurface that define the cavity, electrons move easily and, thus, adischarge phenomenon is more efficiently produced, which improves theresponsivity to ESD. Thus, fluctuations in responsivity to ESD caused bya variation in the distance between discharge electrodes are effectivelyprevented. Therefore, the ESD characteristics are easily adjusted andstabilized.

Since the conductive material that causes creeping discharge ispreferably in contact with both the bottom surface and the top surfacethat define the cavity, the responsivity to ESD can be further improvedas compared to the case in which a conductive material is dispersed ononly one of the surfaces.

Furthermore, since the conductive material is preferably in contact withboth the bottom surface and the top surface that define the cavity,detachment of the conductive material from the substrate body isprevented. Consequently, the degradation of ESD characteristics causedby repetitive discharges (e.g., an increase in discharge startingvoltage) is prevented.

A portion of the conductive material is preferably buried in theinsulating substrate.

In this case, the conductive material is not only in contact with theinsulating substrate, but is also buried in the insulating substrate.Thus, detachment of the conductive material from the insulatingsubstrate is more effectively prevented.

The insulating substrate is preferably a ceramic substrate including aceramic material and a glass material. The conductive material is fixedto the insulating substrate using the glass material.

In this case, the conductive material is not only in contact with theinsulating substrate, but is also fixed using the glass material. Thus,detachment of the conductive material from the insulating substrate ismore effectively prevented.

When a glass layer is made of a glass material provided on an innercircumferential surface that defines the cavity, the surface roughnessof the inner circumferential surface that defines the cavity isdecreased. Therefore, the distance that electrons move during creepingdischarge is decreased, and, thus, the responsivity to ESD is furtherimproved.

According to another preferred embodiment of the present invention, asupporting electrode portion is preferably formed by disposingconductive material powder, which is the supporting electrode material,along an inner surface that defines the cavity between the exposedportions of the discharge electrodes, the conductive material powderbeing disposed in a single layer such that only a single particle of theconductive material powder is included in a thickness direction.

In the above-described configuration, the conductive material powder ofthe supporting electrode portion may preferably be disposed below theinner surface that defines the cavity so as not to be exposed at all inthe cavity or may preferably protrude from the inner surface thatdefines the cavity into the cavity so as to be partly exposed in thecavity.

In the above-described configuration, the conductive material powder ofthe supporting electrode portion may preferably be disposed in a uniformdensity, or may preferably be disposed in a non-uniform density, forexample, in the form of a belt defined by a single row or a plurality ofrows, a mesh, or an island, for example.

In the above-described configuration, by adjusting the amount and typeof conductive material of the supporting electrode portion, thedischarge starting voltage can be set to a desired voltage. Thus, thedischarge starting voltage can be set with high precision as compared tothe case in which a discharge starting voltage is adjusted only bychanging the distance between the discharge electrodes arranged to faceeach other. Since the conductive material powder of the supportingelectrode portion is disposed in a single layer such that only a singleparticle of the conductive material powder is provided in a thicknessdirection, the probability that particles of the conductive materialpowder of the supporting electrode portion contact each other isdecreased and the generation of short circuits between the dischargeelectrodes is prevented. Thus, the short-circuit resistance iseffectively improved.

Furthermore, by forming the supporting electrode portion along the innersurface of the cavity using a conductive material that is the same as orsimilar to the material of the discharge electrodes, the differences inshrinkage behavior and coefficient of thermal expansion between thesupporting electrode portion and the discharge electrodes are reduced ina region between the discharge electrodes. As a result, failure orcharacteristic variations due to, for example, detachment of thedischarge electrodes or changes in characteristics over time areprevented.

At least a portion of the conductive material powder of the supportingelectrode portion is preferably exposed in the cavity from the innersurface that defines the cavity.

In this case, by exposing the conductive material of the dischargeelectrodes, creeping discharge is further promoted and the ESDcharacteristics are further improved. For example, the dischargestarting voltage is decreased and the responsivity to ESD is improved.

The conductive material powder of the supporting electrode portion ispreferably coated with a non-conductive material.

In this case, contact between particles of the conductive materialpowder of the supporting electrode portion is easily prevented.

The supporting electrode portion preferably includes a portion arrangedalong an interface between the insulating substrate and the dischargeelectrodes.

In the above-described configuration, the alignment precision betweenthe supporting electrode portion and the discharge electrodes isimproved as compared to the case in which a supporting electrode portionis provided in only a certain region between the exposed portions of thedischarge electrodes. Consequently, variations in discharge startingvoltage are decreased and the production cost is effectively reduced.

The insulating substrate is preferably a ceramic substrate.

In the above-described configuration, by providing the supportingelectrode portion along the inner surface of the cavity using aconductive material whose shrinkage behavior during firing is the sameas or similar to the material of the discharge electrodes, thedifference in the shrinkage behavior between the discharge electrodesand the ceramic substrate is reduced near a region between the exposedportions of the discharge electrodes. As a result, failure andcharacteristic variation due to, for example, detachment of thedischarge electrodes during firing are prevented. In addition, thevariation in discharge starting voltage is prevented because thevariation in the distance between the discharge electrodes is alsoprevented.

The coefficient of thermal expansion around the supporting electrodeportion may preferably be adjusted to an intermediate value between thatof the discharge electrodes and that of the ceramic substrate. Thisreduces the difference in a coefficient of thermal expansion between thedischarge electrodes and the ceramic substrate in the supportingelectrode portion, thereby preventing failure due to detachment of thedischarge electrodes and changes in characteristics over time.

A method for manufacturing an ESD protection device according to anotherpreferred embodiment of the present invention preferably includes afirst step of forming at least a pair of discharge electrodes on atleast one of a principal surface of a first insulating layer and aprincipal surface of a second insulating layer, the pair of dischargeelectrodes being arranged with a space therebetween, a second step ofattaching, in a dispersed manner, a supporting electrode material havingconductivity to a portion between the pair of discharge electrodesformed on the one of the principal surface of the first insulating layerand the principal surface of the second insulating layer, a third stepof laminating the first insulating layer and the second insulating layerwhile the principal surface of the first insulating layer and theprincipal surface of the second insulating layer face each other, and afourth step of forming external electrodes on a surface of a laminatedbody obtained through the third step such that the external electrodesare connected to the discharge electrodes. A cavity is formed betweenthe first insulating layer and the second insulating layer inside thelaminated body, the pair of discharge electrodes each includes a portionexposed in the cavity, and the supporting electrode material is disposedin the cavity in a dispersed manner.

In the above-described method, an ESD protection device can be easilymanufactured in which the supporting electrode material is dispersedbetween the discharge electrodes that face each other in the cavity andESD characteristics can be adjusted and stabilized.

A method for manufacturing an ESD protection device according to anotherpreferred embodiment of the present invention preferably includes afirst step of attaching a conductive material to a principal surface ofa first insulating layer in a dispersed manner, a second step of formingat least a pair of discharge electrodes on the principal surface of thefirst insulating layer, the discharge electrodes being arranged with aspace therebetween, so that at least a portion of the conductivematerial attached to the principal surface of the first insulating layeris exposed between the discharge electrodes, a third step of laminatinga second insulating layer on the principal surface of the firstinsulating layer so that a principal surface of the second insulatinglayer covers the discharge electrodes and is in contact with theconductive material, and a fourth step of forming external electrodes ona surface of a laminated body obtained through the third step such thatthe external electrodes are connected to the discharge electrodes. Acavity is formed between the principal surface of the first insulatinglayer and the principal surface of the second insulating layer. The pairof discharge electrodes each preferably includes a portion that isexposed in the cavity. In the cavity, the conductive material is incontact with the principal surface of the first insulating layer and theprincipal surface of the second insulating layer, and a gap is formedbetween particles of the conductive material.

In the above-described method, the principal surface of the firstinsulating layer and the principal surface of the second insulatinglayer define the top surface and the bottom surface that define thecavity. Therefore, the conductive material can be easily formed so as tobe in contact with the top surface and the bottom surface that definethe cavity.

In the third step, a portion of the conductive material is preferablyburied in at least one of the first insulating layer and the secondinsulating layer by press-bonding the principal surface of the secondinsulating layer onto the principal surface of the first insulatinglayer.

In this case, the conductive material is not only in contact with theinsulating substrate, but is also buried in the insulating substrate.Thus, detachment of the conductive material from the insulatingsubstrate is more effectively prevented.

Each of the first insulating layer and the second insulating layer arepreferably primarily made of a ceramic material. The above-describedmethod preferably includes a step of firing the laminated body obtainedthrough the third step.

In this case, an ESD protection device can be easily manufactured by thesame method as that of a ceramic multilayer substrate. Herein, the stepof firing the laminated body may be performed before or after the fourthstep.

In the step of firing the laminated body, the conductive material ispreferably buried in at least one of the first insulating layer and thesecond insulating layer by shrinking the laminated body in a laminationdirection.

In this case, the conductive material can be buried by using theshrinkage caused when the first insulating layer and the secondinsulating layer, each primarily made of a ceramic material, are fired.

Preferably, at least one of the first insulating layer and the secondinsulating layer includes a glass material, and, in the step of firingthe laminated body, a glass layer made of the glass material is formedin a region of the principal surface of the insulating layer, the regionfacing a portion to be the cavity.

In this case, the conductive material can be fixed to the insulatinglayer more securely due to the diffusion of the glass material.Furthermore, since the surface roughness of the inner circumferentialsurface that defines the cavity is decreased, the distance thatelectrons move during creeping discharge is decreased, and, thus, theresponsivity to ESD is further improved.

In the first step, a gap-forming material dispersed together with theconductive material is preferably attached to the principal surface ofthe first insulating layer. The gap is formed between particles of theconductive material by eliminating the gap-forming material from thelaminated body obtained through the third step.

In this case, the gap is preferably formed between particles of theconductive material through the elimination of the gap-forming materialand, thus, the generation of short circuits caused between the dischargeelectrodes by the contact between adjacent particles of the conductivematerial is effectively prevented.

In the first step, the conductive material and the gap-forming materialare preferably attached to the principal surface of the first insulatinglayer in a mixed arrangement.

In this case, the conductive material is easily disposed in the cavityin a dispersed manner.

In the first step, a mixed material of chargeable powder including theconductive material and chargeable powder including the gap-formingmaterial is preferably attached to the principal surface of the firstinsulating layer by xerography.

In this case, a uniformly dispersed conductive material and gap-formingmaterial can be attached to the principal surface of the firstinsulating layer. Thus, the distance between particles of the conductivematerial can be ensured with certainty and stable responsivity to ESD isachieved.

In the mixed material, the content of the chargeable powder includingthe conductive material is preferably between about 20% and about 80%,for example.

When the content of the chargeable powder including the conductivematerial is about 20% or greater, satisfactory ESD dischargecharacteristics are easily achieved due to the conductive material. Whenthe content of the chargeable powder including the conductive materialis about 80% or less, a gap having a sufficient size can be formedbetween particles of the conductive material and, thus, short circuitsbetween the discharge electrodes are effectively prevented.

A method for manufacturing an ESD protection device according to anotherpreferred embodiment of the present invention preferably includes afirst step of forming a supporting electrode portion by disposingconductive material powder in a single layer such that only a singleparticle of the conductive material powder is provided in a thicknessdirection, the conductive material powder being disposed on a principalsurface of a first insulating layer, a second step of forming at least apair of discharge electrodes on the principal surface of the firstinsulating layer so that at least one portion of the supportingelectrode portion is exposed between the discharge electrodes, a thirdstep of forming a second insulating layer on the principal surface ofthe first insulating layer so that the second insulating layer coats thedischarge electrodes and covers an exposed region in which the at leastone portion of the supporting electrode portion is exposed between thedischarge electrodes, the second insulating layer being separated fromthe exposed region, and a fourth step of forming external electrodes ona surface of a laminated body obtained through the third step such thatthe external electrodes are connected to the discharge electrodes. Acavity surrounded by the second insulating layer, the dischargeelectrodes, and the exposed region is formed.

In the above-described method, the conductive material powder beingexposed in the cavity is easily formed.

Specifically, the conductive material powder may preferably be formed bythe various methods described below.

In the second step, a cavity-forming layer including an eliminationmaterial is preferably formed on at least one portion of the supportingelectrode portion that is to be exposed between the dischargeelectrodes. After the second insulating layer is formed on thecavity-forming layer in the third step, the cavity is formed byeliminating at least one portion of the cavity-forming layer.

In the first step, the supporting electrode portion is preferably formedby transferring, onto the first insulating layer, conductive materialpowder disposed in a single layer such that only a single particle ofthe conductive material powder is provided in a thickness direction.

In the first step, the supporting electrode portion is preferably formedby xerography.

In the first step, the conductive material powder of the supportingelectrode portion disposed on the principal surface of the firstinsulating layer and in a single layer such that only a single particleof the conductive material powder is provided in a thickness direction,is preferably coated with an elimination material.

In this case, the contact between particles of the conductive materialpowder of the supporting electrode portion can be easily prevented.

According to a preferred embodiment of the present invention, the ESDcharacteristics of an ESD device are easily adjusted and stabilized.

According to another preferred embodiment of the present invention, theESD characteristics of an ESD device are easily adjusted and stabilizedand thus the degradation of discharge characteristics caused byrepetitive discharges are prevented.

According to yet another preferred embodiment of the present invention,the discharge starting voltage can be set with high precision and an ESDprotection device having high reliability can be manufactured.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of an ESD protection device according to apreferred embodiment of the present invention.

FIG. 2 is an enlarged sectional view of a cavity in the ESD protectiondevice shown in FIG. 1.

FIG. 3 is a conceptual diagram after a supporting electrode is formed inthe ESD protection device shown in FIG. 1.

FIG. 4 is a sectional view showing a production process of an ESDprotection device according to a preferred embodiment of the presentinvention.

FIG. 5 is an explanatory view of discharge in an ESD protection device.

FIG. 6 is an explanatory view of a cavity.

FIG. 7 is a sectional view of an ESD protection device according toanother preferred embodiment of the present invention.

FIG. 8 is an enlarged sectional view of a cavity in the ESD protectiondevice shown in FIG. 7.

FIG. 9 is an enlarged sectional view of a cavity according to apreferred embodiment of the present invention.

FIG. 10 is a conceptual diagram after a supporting electrode is formedin the ESD protection device shown in FIG. 9.

FIG. 11 is an enlarged sectional view of a cavity according to anotherpreferred embodiment of the present invention.

FIG. 12 is a conceptual diagram after a supporting electrode is formedin the ESD protection device shown in FIG. 11.

FIGS. 13A to 13D are conceptual diagrams after a supporting electrode isformed according to various preferred embodiments of the presentinvention.

FIGS. 14A and 14B are sectional views showing a production process of anESD protection device according to another preferred embodiment of thepresent invention.

FIG. 15 is a sectional view of an ESD protection device of a ComparativeExample 1.

FIG. 16 is an enlarged sectional view of a principal portion of asupporting electrode of the Comparative Example 1.

FIG. 17 is an explanatory view of discharge of the Comparative Example1.

FIG. 18 is a sectional view of an ESD protection device according toanother preferred embodiment of the present invention.

FIG. 19 is an enlarged sectional view of a principal portion of the ESDprotection device shown in FIG. 18.

FIG. 20 is a sectional view taken along line A-A of FIG. 18.

FIG. 21 is a sectional view of an ESD protection device according toanother preferred embodiment of the present invention.

FIG. 22 is a sectional view of an ESD protection device according toanother preferred embodiment of the present invention.

FIG. 23 is a graph showing ESD characteristics of a preferred embodimentof the present invention and a Comparative Example 2.

FIG. 24 is an enlarged sectional view of a principal portion of a cavityaccording to another preferred embodiment of the present invention.

FIG. 25 is a sectional view of an ESD protection device according toanother preferred embodiment of the present invention.

FIGS. 26A and 26B are sectional views showing a production process of anESD protection device according to another preferred embodiment of thepresent invention.

FIG. 27 is a sectional view of an ESD protection device the ComparativeExample 2.

FIG. 28 is an enlarged sectional view of a principal portion of the ESDprotection device of the Comparative Example 2.

FIG. 29 is a sectional view of an ESD protection device according toanother preferred embodiment of the present invention.

FIG. 30 is an enlarged sectional view of a principal portion of asupporting electrode portion according to another preferred embodimentof the present invention.

FIG. 31 is a perspective view of discharge electrodes and a supportingelectrode portion according to another preferred embodiment of thepresent invention.

FIG. 32 is an enlarged sectional view of a principal portion of asupporting electrode portion according to another preferred embodimentof the present invention.

FIG. 33 is a sectional view of an ESD protection device according toanother preferred embodiment of the present invention.

FIGS. 34A and 34B are sectional views of a principal portion of asupporting electrode portion according to another preferred embodimentof the present invention.

FIG. 35 is a sectional view of an ESD protection device of a ComparativeExample 3.

FIG. 36 is an enlarged sectional view of a principal portion of thesupporting electrode portion of the Comparative Example 3.

FIG. 37 is an exploded perspective view of a known ESD protectiondevice.

FIG. 38 is a sectional view of the known ESD protection device shown inFIG. 37.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be describedwith reference to FIGS. 1 to 36.

Example 1-1

An ESD protection device 10 of an Example 1-1 of a preferred embodimentof the present invention will be described with reference to FIGS. 1 to6.

FIG. 1 is a sectional view of an ESD protection device 10. As shown inFIG. 1, the ESD protection device 10 preferably includes a cavity 13provided in a substrate body 12 of a ceramic substrate. A pair ofdischarge electrodes 16 and 18 are arranged such that the respectiveedges 16 k and 18 k are exposed in the cavity 13. The dischargeelectrodes 16 and 18 are arranged so that the edges 16 k and 18 k faceeach other with a space provided therebetween. The discharge electrodes16 and 18 extend to the peripheral surface of the substrate body 12 andare respectively connected to external electrodes 22 and 24 provided onthe surface of the substrate body 12. The external electrodes 22 and 24are used to connect the ESD protection device 10 to another device.

As schematically shown in FIG. 1, a plurality of supporting electrodeparticles 15 obtained by coating the surface of particulate supportingelectrode material 30 having conductivity with an insulating material 32are disposed in the cavity 13. That is, the particulate supportingelectrode material 30 having conductivity is dispersed in the cavity 13.

FIG. 2 is an enlarged sectional view of the cavity 13. As schematicallyshown in FIG. 2, a top surface 13 p and a bottom surface 13 s thatdefine the cavity 13 are respectively defined by sealing members 14 pand 14 s. The sealing members 14 p and 14 s are disposed between thesubstrate body 12 and the cavity 13 and prevent the glass component inthe substrate body 12, which is a ceramic substrate, from entering thecavity 13. The sealing members 14 p and 14 s have an insulatingproperty.

In the ESD protection device 10, when a voltage equal to or greater thana certain voltage is applied between the external electrodes 22 and 24,discharge is generated between the discharge electrodes 16 and 18 thatface each other in the cavity 13.

A method for manufacturing the ESD protection device 10 will bedescribed with reference to a conceptual diagram of FIG. 3 and aschematic view of FIG. 4.

First, materials for forming a substrate body 12, discharge electrodes16 and 18, and sealing members 14 p and 14 s are prepared.

A ceramic green sheet for forming the substrate body 12 is prepared. Amaterial primarily including Ba, Al, and Si (BAS material) is preferablyused as a ceramic material. Raw materials are prepared and mixed so thatthe mixture has a desired composition, and then calcined at about 800°C. to about 1000° C. The calcined powder is pulverized using a zirconiaball mill for about 12 hours to obtain ceramic powder. An organicsolvent, such as toluene or EKINEN, for example, is preferably added tothe BAS material-calcined ceramic powder and mixed. A binder and aplasticizer are further added thereto and mixed to obtain a slurry. Theobtained slurry is molded on a PET film by a doctor blade method toobtain a ceramic green sheet having a desired thickness of about 10 μmto about 50 μm, for example.

An electrode paste for forming the discharge electrodes 16 and 18 isprepared. A solvent is added to about 80 wt % Cu powder having anaverage particle size of about 2 μm, for example, and a binder resinincluding ethyl cellulose or other suitable resin, for example, and themixture is stirred and mixed using a roll mill to obtain an electrodepaste.

A sealing member-forming paste for forming the sealing members 14 p and14 s is prepared by the same or substantially the same method as theelectrode paste. A solvent is added to about 80 wt % Al₂O₃ powder havingan average particle size of about 1 μm, for example, and a binder resincomposed of ethyl cellulose or other suitable resin, for example, andthe mixture is stirred and mixed using a roll mill to obtain a sealingmember-forming paste (alumina paste). The sealing member is defined by amaterial having a sintering temperature greater than that of a substratematerial.

As shown in FIG. 4, the sealing member-forming paste (alumina paste) isapplied by screen printing on surfaces 11 p and 11 s, which arerespectively principal surfaces of ceramic green sheets 11 a and 11 b,to form sealing members 14 p and 14 s. The sealing member-forming pasteis prepared in an amount equivalent to two layers because the sealingmembers 14 p and 14 s are arranged so as to sandwich the dischargeelectrodes 16 and 18 therebetween at their edges 16 k and 18 k in avertical direction.

The discharge electrodes 16 and 18 are formed by screen printing on thesurface 11 s of the ceramic green sheet 11 b, which is at least one theceramic green sheets 11 a and 11 b on which the sealing members 14 p and14 s are formed.

In the production example, the discharge electrodes 16 and 18 werepreferably formed in a belt shape so that the width of each of thedischarge electrodes 16 and 18 was about 100 μm, for example, and thedischarge gap between the edges 16 k and 18 k of the dischargeelectrodes 16 and 18 that face each other was about 30 μm, for example.

As shown in FIG. 3, supporting electrode particles 15 obtained bycoating the surface of a supporting electrode material 30 with aninsulating material 32 are attached, by screen printing or xerography,for example, to the ceramic green sheet 11 b on which the sealing member14 s and the discharge electrodes 16 and 18 have been formed, to form asupporting electrode formation layer 15 k shown in FIG. 4.

In the case of screen printing, a paste including the supportingelectrode material is prepared, and a supporting electrode formationlayer 15 k is formed using the prepared paste, whereby the supportingelectrode material is attached.

The paste including the supporting electrode particles 15 is preferablyprepared by the following method.

Cu powder coated with alumina and having an average particle size ofabout 5 μm, for example, is prepared in a certain ratio. A binder resinand a solvent are added thereto and then stirred and mixed using a rollmill to obtain the paste. The content of the resin and the solvent inthe paste is set to about wt %, for example. The Cu powder coated withalumina is not sintered during firing. That is, necking is not caused.The Cu powder coated with alumina maintains an insulating property evenafter firing.

The height of the cavity 13 can be controlled by adjusting the amount ofthe paste applied.

In the case in which the supporting electrode is formed by xerography, atoner including supporting electrode particles 15 is prepared, and thena supporting electrode formation layer is formed using the preparedtoner.

The toner is prepared as follows.

1. Cu powder coated with alumina having an average particle size ofabout 5 μm and a resin are mixed with each other, and the surface of theCu powder coated with alumina is covered with the resin using asurface-treating machine.

2. The sample obtained through the process 1 is classified to removefine powder and coarse powder.

3. The capsulated Cu powder obtained through the process and an externaladditive are mixed with each other, and the external additive isuniformly attached to the surface of the capsulated Cu powder using asurface-treating machine.

4. The capsulated Cu powder obtained through the process 3 and a carrierare mixed with each other to obtain a toner, which is a developer.

The supporting electrode is formed as follows.

1. A photoconductor is uniformly charged.

2. The charged photoconductor is irradiated with light using an LED in apattern of a supporting electrode, to form a latent image.

3. A development bias is applied to develop the toner on thephotoconductor. The amount of the toner applied can be controlled inaccordance with the magnitude of the development bias.

4. A ceramic green sheet is disposed on the photoconductor on which thepattern of a supporting electrode has been developed, to transfer thetoner onto the sealing member 14 s of the ceramic green sheet 11 b.

5. The ceramic green sheet onto which the pattern of a supportingelectrode has been transferred is inserted into an oven to fix thetoner. Thus, a ceramic green sheet having a pattern of a supportingelectrode is obtained.

Note that the supporting electrode itself maintains an insulatingproperty even after firing.

As indicated by an arrow 11 x in FIG. 4, the ceramic green sheets 11 aand 11 b are laminated and press-bonded with each other such that thesurfaces 11 p and 11 s of the ceramic green sheets 11 a and 11 b onwhich the sealing members 14 p and 14 s have been formed face each otherand the sealing members 14 p and 14 s sandwich the supporting electrodeformation layer 15 k. Thus, a laminated body is formed.

In this production example, the ceramic green sheets were laminated witheach other so that the thickness of the laminated body was about 0.35mm, for example, and the discharge electrodes and the supportingelectrode formation layer were arranged in the center in the thicknessdirection.

In the case in which a laminated body including a plurality of ESDprotection devices is formed, the laminated body is cut into chips usinga die in the same or substantially the same manner as in a chip-typecomponent, such as an LC filter. In this production example, thelaminated body was cut into chips each having a size of about 1.0mm×about 0.5 mm. After that, the electrode paste is applied to the endsurfaces of each of the chips to form external electrodes.

The chip having the external electrodes formed thereon is fired in a N2atmosphere in the same or substantially the same manner as in a typicalceramic multilayer component. The resin component and the solventcomponent included in the supporting electrode formation layer 15 ksandwiched between the ceramic green sheets are eliminated during thefiring, and thus, a space defining the cavity 13 is formed.

In the case in which an inert gas, such as Ar or Ne, for example, isintroduced into the cavity 13 to decrease the response voltage to ESD,firing may be performed in an atmosphere of an inert gas, such as Ar orNe, for example, in a temperature range in which a ceramic material isshrunk and sintered. If the electrode material is not oxidized (e.g.,Ag), the firing may be performed in the air.

Electrolytic Ni plating and Sn plating are performed on the externalelectrodes of the fired chip in the same or substantially the samemanner as in a chip-type component, such as an LC filter to complete anESD protection device.

As described above, an ESD protection device can be easily manufacturedusing a ceramic substrate.

The ceramic material of the substrate body 12 is not particularlylimited to the above-described material as long as the ceramic materialhas an insulating property. Therefore, such a ceramic material maypreferably be a mixture of forsterite and glass, a mixture of CaZrO₃ andglass, or other suitable material, for example.

The electrode material of the discharge electrodes 16 and 18 is also notlimited to Cu, and may preferably be Ag, Pd, Pt, Al, Ni, W, or acombination thereof, for example.

The supporting electrode material 30 is preferably at least oneconductive material selected from transition metals, such as Cu, Ni, Co,Ag, Pd, Rh, Ru, Au, Pt, and Ir, for example. These metals may be usedalone or in a form of an alloy. Furthermore, a resistive metal oxide ofthese metals or a semiconductor material, such as SiC, for example, maypreferably be used.

Supporting electrode particles 15 are preferably formed by coating thesurface of the supporting electrode material 30 with an inorganicmaterial, such as Al₂O₃, ZrO₂, or SiO₂, a mixed calcined material suchas BAS, or an insulating material 32, such as high melting point glass,for example. The insulating material 32 that coats the surface of thesupporting electrode material 30 is used to prevent the sintering of thesupporting electrode material 30. Any material may be used as long asthe material has an insulating property.

The average particle size of the supporting electrode material 30 ispreferably in a range of about 0.05 μm to about 10 μm, and morepreferably about 1 μm to about 5 μm, for example. As the particle sizeis decreased, the surface area is increased, which leads to a decreasein discharge starting voltage. As a result, the responsivity to ESD isimproved and the degradation of discharge characteristics is reduced.

The sealing members 14 p and 14 s are preferably made of a ceramicmaterial having a sintering temperature greater than that of the ceramicmaterial used for the substrate body 12. Any material, such as anitride, for example, may be used as long as the material prevents glassfrom entering from the substrate body 12 and the material itself doesnot produce glass.

Since the supporting electrode material 30 is dispersed in the cavity 13in the ESD protection device 10 of Example 1-1, the discharge startingvoltage is decreased and the responsivity to ESD is improved.

In other words, a discharge phenomenon that occurs between dischargeelectrodes that face each other is primarily creeping discharge that isgenerated along the interface between a cavity (gas phase) and asubstrate (insulator). It is to be noted that other discharge phenomenaalso occur. Creeping discharge is a discharge phenomenon in whichcurrent flows along a surface of a material (insulator). Although it hasbeen described that electrons flow, it is believed that, in reality, theelectrons move by hopping along the surface and ionizing the gas. Thepresence of conductive powder on the surface of an insulator decreasesthe distance which the electrons hop and imparts directionality to theelectrons, thereby generating creeping discharge more actively.

In the ESD protection device 10 of Example 1-1, the supporting electrodeparticles 15 obtained by coating the surface of the supporting electrodematerial 30 having conductivity with the insulating material 32 aredispersed in a space between the discharge electrodes 16 and 18 facingeach other, and the space is filled with the supporting electrodeparticles 15. In a portion in which the supporting electrode particles15 are disposed, that is, in the supporting electrode, the supportingelectrode material 30 is present in a state in which the supportingelectrode material 30 is not sintered after firing, that is, in whichnecking is not caused. The supporting electrode particles 15 includingthe supporting electrode material 30 are simply stacked on top of eachother, that is, are simply in contact with each other. As a result, agap 15 y is present between the supporting electrode particles 15 asshown in FIG. 6.

In the configuration of Example 1-1, creeping discharge is generatedalong the surfaces of the stacked supporting electrode particles 15,that is, in a gap between the surface of the insulating material 32 thatcoats the surface of the supporting electrode material 30 and theadjacent supporting electrode particle 15. In Example 1-1, as indicatedby arrows 82, 84, and 86 in an explanatory view of FIG. 5, there aremany paths of creeping discharge. Thus, creeping discharge is moreeasily generated as compared to Comparative Example 1 described later.That is, a discharge phenomenon can be efficiently produced. Therefore,the distance between the discharge electrodes 16 and 18 can bedecreased, and the fluctuation in responsivity to ESD caused byvariations in the distance between the discharge electrodes 16 and 18 isreduced.

In the configuration of Example 1-1, since the gap between thesupporting electrode particles 15 is minute, a loss caused by gaseousdischarge is reduced as compared to in Comparative Example 1. Therefore,the degradation of discharge characteristics can be reduced comparedwith in Comparative Example 1.

Furthermore, by adjusting the amount and particle size of a supportingelectrode material dispersed in the cavity, desired ESD characteristics,e.g., discharge starting voltage, can be easily achieved.

Therefore, the ESD characteristics can be easily adjusted andstabilized.

The sealing members 14 p and 14 s prevent a glass component fromentering from the ceramic substrate body 12. Thus, the sealing members14 p and 14 s prevent the insulating material 32 that coats thesupporting electrode material 30 from being eroded by a glass componentand, therefore, the supporting electrode material 30 from beingsintered, and also prevent the supporting electrode material 30 fromdiffusing into the ceramic substrate body 12. As a result, the gapbetween the supporting electrode particles 15 is maintained, and the ESDprotection characteristics are improved.

Comparative Example 1

An ESD protection device 10 x of Comparative Example 1 will be describedwith reference to FIGS. 15 to 17.

FIG. 15 is a sectional view of an ESD protection device 10 x. FIG. 16 isan enlarged sectional view of a principal portion that schematicallyshows a region 11 indicated by a chain line in FIG. 15. FIG. 17 is anexplanatory view of discharge.

As shown in FIG. 15, the ESD protection device 10 x includes a cavity 13x provided in a substrate body 12 x of a ceramic multilayer substratesuch that portions 17 and 19 of discharge electrodes 16 and 18 areexposed in the cavity 13 x in a similar manner as in Example 1-1. Thedischarge electrodes 16 and 18 are respectively connected to externalelectrodes 22 and 24 provided on a surface of the substrate body 12 x.

In the ESD protection device 10 x, unlike in Example 1-1, a supportingelectrode 14 x is arranged so as to be adjacent to a portion between thedischarge electrodes 16 and 18. As shown in FIG. 16, the supportingelectrode 14 x is a region in which a metal material 20 x is dispersedin an insulating material defining the substrate body 12 x and has anoverall insulating property. A portion of the metal material 20 x isexposed in the cavity 13 x. The supporting electrode 14 x is formed byapplying a paste for a supporting electrode that includes, for example,a ceramic material and a metal material to a ceramic green sheet.

In Comparative Example 1, as indicated by an arrow 80 in FIG. 17,creeping discharge is generated along the interface between thesupporting electrode 14 x and the cavity 13 x.

If the metal material 20 x of the supporting electrode 14 x that isexposed in the cavity 13 x is detached due to the impact of discharge,the discharge characteristics are degraded. Therefore, the dischargecharacteristics are easily degraded in Comparative Example 1.

For production examples of the ESD protection devices of ComparativeExample 1 and Example 1-1, the ESD protection characteristics werecompared to each other.

Specifically, in the production example of Example 1-1, a supportingelectrode formation portion was formed by screen printing. In theproduction example of Comparative Example 1, a supporting electrode wasformed by screen printing using a paste including a metal material. Inthe production examples of Example 1-1 and Comparative Example 1, thesame size, shape, and firing conditions were used except for thesupporting electrodes.

One hundred samples of each of Example 1-1 and Comparative Example 1were evaluated for the discharge responsivity to ESD between dischargeelectrodes. The discharge responsivity to ESD was measured using anelectrostatic discharge immunity test provided in IEC61000-4-2, which isthe standard of IEC. When a voltage of about 2 kV to about 8 kV wasapplied through contact discharge, whether or not discharge wasgenerated between the discharge electrodes of the samples was measured.

Table 1 shows the comparison results.

TABLE 1 Table 1 Comparison of supporting electrode structures Dischargeresponsivity to ESD 1 kV 2 kV 4 kV 6 kV 8 kV Comparative Example 1 — — —D D Example 1 D D D D D

In Table 1, “D” indicates that discharge was generated between thedischarge electrodes of the samples and the ESD protection functionoccurred.

As is clear from Table 1, the discharge responsivity to ESD issignificantly better in Example 1-1 in which the supporting electrodematerial is dispersed in the cavity than in Comparative Example 1 inwhich the supporting electrode including the metal material dispersedtherein is formed so as to be adjacent to the cavity. Therefore, the ESDprotection characteristics are improved in Example 1-1.

Modification 1-1

A Modification 1-1 of a preferred embodiment of the present inventionwill be described with reference to FIGS. 7 and 8.

Modification 1-1 is a modification of Example 1-1. Hereinafter, the sameelements and components as those in Example 1-1 are designated by thesame reference numerals, and the differences between Example 1-1 andModification 1-1 will be primarily described.

FIG. 7 is a sectional view of an ESD protection device 10 a ofModification 1-1. FIG. 8 is an enlarged sectional view of a principalportion that shows a cavity 13 a of the ESD protection device 10 a ofModification 1-1.

As shown in FIGS. 7 and 8, in the ESD protection device 10 a ofModification 1-1, the height of the cavity 13 a including a supportingelectrode material dispersed therein is substantially equal to thethickness of the discharge electrodes 16 and 18. In other words, asealing member 14 q that defines a top surface 13 q of the cavity 13 aextends so as to have a planar shape.

Creeping discharge is most easily generated in the boundary portionbetween the ceramic substrate body 12 and the supporting electrode. Inthe ESD protection device 10 a of Modification 1-1, by reducing theheight of the cavity 13 a, the distance of the boundary portion thatconnects the discharge electrodes 16 and 18 is decreased. Thus, the ESDprotection characteristics are further improved.

Example 1-2

An ESD protection device of an Example 1-2 of a preferred embodiment ofthe present invention will be described with reference to FIGS. 9 and10.

The ESD protection device of Example 1-2 has substantially the sameconfiguration as that of the ESD protection device 10 of Example 1-1.Hereinafter, the same elements and components as those in Example 1-1are designated by the same reference numerals, and the differencesbetween Example 1-1 and Example 1-2 will be primarily described.

FIG. 9 is an enlarged sectional view of a principal portion of a cavity13. As shown in FIG. 9, the ESD protection device of Example 1-2 isdifferent from the ESD protection device 10 of Example 1-1 in that, inaddition to the supporting electrode particles 15 including a supportingelectrode material, insulating particles 15 s are dispersed in thecavity 13. That is, the supporting electrode includes a mixture of thesupporting electrode particles 15 and the insulating particles 15 s. Theparticles 15 and 15 s that are disposed in the cavity and that definethe supporting electrode need to be not sintered with each other and,thus, have an insulating property.

The supporting electrode material included in the supporting electrodeparticles 15 is preferably at least one metal selected from transitionmetals, such as Cu, Ni, Co, Ag, Pd, Rh, Ru, Au, Pt, and Ir, for example.These metals may be used alone or in a form of an alloy. Furthermore, ametal oxide of these metals may be used. Alternatively, a semiconductormaterial, such as SiC, for example, may be used as the supportingelectrode material of the supporting electrode particles. Metalparticles and semiconductor particles may be used in a mixed manner.

In Example 1-2, since an insulating property of the discharge electrodescan be ensured by disposing the insulating particles 15 s between thesupporting electrode particles 15, the supporting electrode particles 15may include only a supporting electrode material having conductivity.

Supporting electrode particles obtained by coating the surface of asupporting electrode material with an insulating material are preferablyused because the insulation reliability of discharge electrodes isimproved. To prevent the sintering of conductive powder, an inorganicmaterial, such as Al₂O₃, ZrO₂, or SiO₂, a mixed calcined material suchas BAS, or a coating material having an insulating property such as highmelting point glass, for example, is preferably used as the insulatingmaterial that coats the supporting electrode material.

Any insulating particles may be used as the insulating particles 15 s aslong as the insulating particles are not sintered with the supportingelectrode particles 15 and also are not sintered with each other. Forexample, the insulating particles 15 s are preferably made of aninorganic material, such as ceramic powder, for example, Al₂O₃, ZrO₂, orSiO₂ having a sintering temperature greater than the firing temperatureof a substrate.

A method for manufacturing the ESD protection device of Example 1-2 willnow be described.

A ceramic green sheet for forming a substrate body, an electrode pastefor forming discharge electrodes, and a sealing member-forming paste forforming a sealing member are prepared by the same or substantially thesame method as in Example 1-1.

A sealing member is formed on a ceramic green sheet using the sealingmember-forming paste by the same or substantially the same method as inExample 1-1.

Discharge electrodes are formed on the ceramic green sheet using theelectrode paste by the same or substantially the same method as inExample 1-1.

A supporting electrode formation layer is formed by screen printing orxerography on the green sheet on which the sealing member and thedischarge electrodes have been formed.

In the case of screen printing, a paste including supporting electrodeparticles and insulating particles is prepared, and a supportingelectrode formation layer is formed using the prepared paste by the sameor substantially the same method as in Example 1-1.

The paste including the supporting electrode particles and theinsulating particles is prepared by the following method.

Cu powder coated with alumina and having an average particle size ofabout 5 μm, for example, and alumina powder are prepared in a desiredratio. A binder resin and a solvent are added thereto and then stirredand mixed using a roll mill to obtain the paste. The ratio of the Cupowder coated with alumina to the alumina powder is preferably set to1:1 by volume, for example. The content of the resin and the solvent inthe paste is preferably set to about 40 wt %, for example. The Cu powdercoated with alumina and the alumina powder are not sintered duringfiring. That is, necking is not caused. The Cu powder coated withalumina and the alumina powder maintain an insulating property evenafter firing.

In the case in which the supporting electrode is formed by xerography, atoner including supporting electrode particles and insulating particlesis prepared, and then a supporting electrode formation layer is formedusing the prepared toner by the same or substantially the same method asin Example 1-1.

The toner including the supporting electrode particles and theinsulating particles is prepared by the following method.

1. Cu powder coated with alumina having an average particle size ofabout 5 μm and a resin are mixed with each other, and the surface of theCu powder is covered with the resin using a surface-treating machine.

2. The sample obtained through the process 1 is classified to removefine powder and coarse powder.

3. The capsulated Cu powder obtained through the process and an externaladditive are mixed with each other, and the external additive isuniformly attached to the surface of the capsulated Cu powder using asurface-treating machine.

4. The capsulated Cu powder obtained through the process 3 and a carrierare mixed with each other to obtain a developer.

5. An alumina powder toner prepared in the same procedure is mixed withthe Cu powder toner in a ratio of 1:1 by volume.

The ceramic green sheets are laminated and press-bonded with each otherby the same or substantially the same method as in Example 1-1 to form alaminated body.

By the same method as in Example 1-1, the laminated body is cut intochips and external electrodes are formed.

Each of the chips having the external electrodes formed thereon is firedby the same or substantially the same method as in Example 1-1.

Electrolytic Ni plating and Sn plating are performed on the externalelectrodes of the fired chip in the same or substantially the samemanner as in Example 1-1 to complete an ESD protection device.

In the ESD protection device of Example 1-2, the ESD protectioncharacteristics are improved due to the supporting electrode particles15 as in Example 1-1.

Furthermore, in the ESD protection device of Example 1-2, by adding theinsulating particles 15 s, such as a insulating green ceramic material,the insulation reliability of the supporting electrode is furtherimproved as compared to in Example 1-1.

Modification 1-2

A Modification 1-2 of a preferred embodiment of the present inventionwill be described with reference to FIG. 11.

Modification 1-2 is a modification of Example 1-2. In the ESD protectiondevice of Modification 1-2, as shown in an enlarged sectional view of aprincipal portion of FIG. 11, the height of a cavity 13 a includingsupporting electrode particles 15 and insulating particles 15 sdispersed therein is substantially equal to the thickness of dischargeelectrodes 16 and 18. In other words, a sealing member 14 q that definesa top surface 13 q of the cavity 13 a extends so as to form a planarshape.

Creeping discharge is most easily generated in the boundary portionbetween the ceramic substrate body 12 and the discharge electrodes 16and 18. In the ESD protection device of Modification 1-2, by reducingthe height of the cavity 13 a, the distance of the boundary portion thatconnects the discharge electrodes 16 and 18 is decreased. Thus, creepingdischarge is more easily generated than in Example 1-2 and the ESDprotection characteristics are further improved.

Example 1-3

An ESD protection device of an Example 1-3 of a preferred embodiment ofthe present invention will be described with reference to FIG. 12.

The ESD protection device of Example 1-3 has substantially the sameconfiguration as that of the ESD protection device 10 of Example 1-1.Hereinafter, the same elements and components as those in Example 1-1are designated by the same reference numerals, and the differencesbetween Example 1-1 and Example 1-3 will be primarily described.

FIG. 12 is a conceptual diagram of a cavity including a supportingelectrode formation layer formed therein before firing. As shown in FIG.12, the ESD protection device of Example 1-3 is different from the ESDprotection device 10 of Example 1-1 in that, in addition to thesupporting electrode particles 15 including a supporting electrodematerial, elimination particles 15 x to be eliminated after firing aredisposed on a sealing member 14. In other words, a supporting electrodeformation layer includes a mixture of the supporting electrode particles15 and the elimination particles 15 x, and after firing, the supportingelectrode particles 15 are dispersed in the cavity.

A method for manufacturing the ESD protection device of Example 1-3 willnow be described.

A ceramic green sheet for forming a substrate body, an electrode pastefor forming discharge electrodes, and a sealing member-forming paste forforming a sealing member are prepared by the same or substantially thesame method as in Example 1-1.

A sealing member is formed on a ceramic green sheet using the sealingmember-forming paste by the same or substantially the same method as inExample 1-1.

Discharge electrodes are formed on the ceramic green sheet using theelectrode paste by the same or substantially the same method as inExample 1-1.

A supporting electrode formation layer is formed by screen printing orxerography on the green sheet on which the sealing member and thedischarge electrodes have been formed.

In the case of screen printing, a paste including supporting electrodeparticles and elimination particles is prepared, and a supportingelectrode formation layer is formed using the prepared paste by the sameor substantially the same method as in Example 1-1.

The paste including the supporting electrode particles and theelimination particles is prepared by the following method.

1. Cu powder coated with alumina and having an average particle size ofabout 5 μm, for example, and acrylic resin beads are prepared in adesired ratio. A binder resin and a solvent are added thereto and thenstirred and mixed using a roll mill to obtain the paste.

2. The ratio of the Cu powder to the acrylic resin beads is set to about1:1 by volume, for example.

3. The content of the resin and the solvent in the paste is set to about40 wt %, for example.

4. The Cu powder coated with alumina is supporting electrode particlesand maintains an insulating property even after firing.

5. The acrylic resin beads define elimination particles that are to beeliminated during firing.

In the case in which a supporting electrode is formed by xerography, atoner including supporting electrode particles and elimination particlesis prepared, and then a supporting electrode formation layer is formedusing the prepared toner by the same or substantially the same method asin Example 1-1.

The toner including the supporting electrode particles, the insulatingparticles, and the elimination particles is prepared by the followingmethod.

1. Cu powder coated with alumina having an average particle size ofabout 5 μm, for example, which is supporting electrode particles, and aresin are mixed with each other, and the surface of the Cu powder iscovered with the resin using a surface-treating machine.

2. The sample obtained through the process 1 is classified to removefine powder and cohered powder.

3. The capsulated Cu powder obtained through the process and an externaladditive are mixed with each other, and the external additive isuniformly attached to the surface of the capsulated Cu powder using asurface-treating machine.

4. The capsulated Cu powder obtained through the process 3 and a carrierare mixed with each other to obtain a toner, which is a developer.

5. A toner including the acrylic resin beads, which are eliminationparticles, is prepared in the same procedure, and mixed with the tonercontaining the Cu powder coated with alumina in a ratio of about 1:1 byvolume, for example.

By the same or substantially the same method as in Example 1-1, thelaminated body is cut into chips and external electrodes are formed.

Each of the chips having the external electrodes formed thereon is firedby the same or substantially the same method as in Example 1-1.

Electrolytic Ni plating and Sn plating are performed on the externalelectrodes of the fired chip in the same or substantially the samemanner as in Example 1-1 to complete an ESD protection device.

The average particle size of the resin beads is preferably in a range ofabout 0.05 μm to about 10 μm, and more preferably about 1 μm to about 5μm, for example. The elimination particles are not necessarily composedof a resin and may be composed of carbon or other suitable material, aslong as the elimination particles are eliminated during firing.

In the supporting electrode formation layer, which is a mixture ofsupporting electrode particles and resin beads, the particles need to benot sintered with each other and thus have an insulating property.

The supporting electrode material included in the supporting electrodeparticles is preferably at least one metal selected from transitionmetals, such as Cu, Ni, Co, Ag, Pd, Rh, Ru, Au, Pt, and Ir, for example.These metals may be used alone or in a form of an alloy. Furthermore, ametal oxide of these metals or a semiconductor material, such as SiC,for example, may be used. Metal particles and semiconductor particlesmay be used in a mixed arrangement.

The supporting electrode particles need only include a supportingelectrode material. However, to prevent the sintering of the supportingelectrode material, the supporting electrode material is preferablycoated with an inorganic material, such as Al₂O₃, ZrO₂, or SiO₂, a mixedcalcined material such as BAS, or a coating material having aninsulating property such as high melting point glass, for example.

In the ESD protection device of Example 1-3, the ESD protectioncharacteristics is improved due to the supporting electrode particles 15as in Example 1-1.

In the ESD protection device of Example 1-3, the added resin beadsprevent the particles of a discharge supporting electrode fromcontacting each other and, thus, from sintering with each other(necking). Consequently, the insulation reliability of the dischargesupporting electrode is further improved as compared to in Example 1-1.

Even if the elimination particles are eliminated, the supportingelectrode particles and the insulating particles are in contact witheach other in the cavity because the ceramic substrate body is shrunkafter firing and the size of the cavity is decreased. As a result, a gaphaving a proper size is formed.

Example 1-4

An Example 1-4 of a preferred embodiment of the present invention willbe described with reference to FIGS. 13A to 13D.

FIGS. 13A to 13D are conceptual diagrams of a cavity having a supportingelectrode formation layer provided therein before firing. Example 1-4 isdifferent from Examples 1-1 to 1-3 in a manner in which particles aredisposed in a cavity.

In the example shown in FIG. 13A, Cu particles 15 a, which aresupporting electrode particles including a conductive material, aluminaparticles 15 s, which are insulating particles, and acrylic resin beads15 x, which are elimination particles, are preferably dispersed on analumina sealing member 14.

In the example shown in FIG. 13B, Cu particles 15 coated with alumina,which are supporting electrode particles obtained by coating the surfaceof a conductive material with an insulating material, alumina particles15 s, which are insulating particles, and acrylic resin beads 15 x,which are elimination particles, are preferably dispersed on an aluminasealing member 14.

In the example shown in FIG. 13C, SiC particles 15 b, which aresupporting electrode particles including a semiconductor material,alumina particles 15 s, which are insulating particles, and acrylicresin beads 15 x, which are elimination particles, are preferablydispersed on an alumina sealing member 14.

In the example shown in FIG. 13D, Cu particles 15 coated with alumina,which are supporting electrode particles obtained by coating the surfaceof a conductive material with an insulating material, SiC particles 15b, which are supporting electrode particles including a semiconductormaterial, alumina particles 15 s, which are insulating particles, andacrylic resin beads 15 x are preferably dispersed on an alumina sealingmember 14.

The supporting electrode formation layer in which particles are disposedas shown in FIGS. 13A to 13D can be formed by combining the productionmethod of Example 1-2 with that of Example 1-3.

In the ESD protection device of Example 1-4, the ESD protectioncharacteristics are improved due to the supporting electrode particles15 as in Example 1-1.

Furthermore, in the ESD protection device of Example 1-4, by adding theinsulating particles, the insulation reliability of the supportingelectrode is further improved as compared to Example 1-1.

In the ESD protection device of Example 1-4, the added resin beadsprevent the particles of a discharge supporting electrode fromcontacting each other and, thus, from sintering with each other(necking). Consequently, the insulation reliability of the dischargesupporting electrode is further improved as compared to Example 1-1.

Example 1-5

An ESD protection device of an Example 1-5 of a preferred embodiment ofthe present invention will be described with reference to FIGS. 14A and14B.

An ESD protection device of Example 1-5 is different from those ofExamples 1-1 to 1-4 in that the substrate body is a resin substrate.

A method for manufacturing the ESD protection device of Example 1-5 willbe described with reference to an exploded sectional view of FIGS. 14Aand 14B.

A substrate A shown in FIG. 14A is prepared. That is, dischargeelectrodes 16 a and 18 a are formed by stacking Cu foil on a prepreg 11s and patterning the Cu foil through photolithography.

A substrate B schematically shown in FIG. 14B is prepared. That is, atoner 60 including supporting electrode particles is disposed on aprepreg 11 t by xerography as in Example 1-1.

As indicated by an arrow 88, the substrate A, which is completely cured,is disposed on the substrate B, which is semi-cured, and they are bondedto each other through the complete cure of the substrate B. A cavity isformed between an edge 16 t of the discharge electrode 16 a and an edge18 t of the discharge electrode 18 a by the thickness of the Cu foil ofthe substrate A. The toner including supporting electrode particles isdisposed in the cavity.

Note that, after the substrate B is completely cured, the substrate Aand the substrate B may be bonded to each other using an adhesive.

A baking electrode or a conductive resin electrode is formed on the endsurfaces of the bonded substrate, and plating is performed thereon toobtain external electrodes.

Through the processes described above, the ESD protection device ofExample 1-4 is completed.

In the ESD protection device of Example 1-4, the ESD protectioncharacteristics is improved due to the toner 60 including supportingelectrode particles as in Example 1-1.

In the ESD protection device of Example 1-4, the sealing member includedin the ESD protection device of Example 1-1 is unnecessary because glassdoes not enter the cavity from the resin substrate body.

Example 2-1

An ESD protection device 110 of an Example 2-1 of a preferred embodimentof the present invention will be described with reference to FIGS. 18 to20. FIG. 18 is a sectional view of an ESD protection device 110. FIG. 19is an enlarged sectional view of a principal portion that shows a cavity113 of the ESD protection device 110. FIG. 20 is a sectional view takenalong line A-A of FIG. 18.

As shown in FIGS. 18 to 20, the ESD protection device 110 preferablyincludes a cavity 113 provided in a substrate body 112 of a ceramicmultilayer substrate. A pair of discharge electrodes 116 and 118 aredisposed such that the respective edges 116 k and 118 k are exposed inthe cavity 113. The discharge electrodes 116 and 118 extend to theperipheral surface of the substrate body 112 and are respectivelyconnected to external electrodes 122 and 124 provided on the surface ofthe substrate body 112. The external electrodes 122 and 124 are used toconnect the ESD protection device 110 to a device.

As shown in FIGS. 18 to 20, the discharge electrodes 116 and 118 arearranged so that the edges 116 k and 118 k exposed in the cavity 113face each other with a space provided therebetween.

As schematically shown in FIGS. 18 to 20, a conductive material 120 isdisposed in the cavity 113. The conductive material 120 is sandwichedbetween a top surface 114 a and a bottom surface 114 b that define thecavity 113. The conductive material 120 is preferably a powdery materialand is dispersed in the cavity 113. The portion in which the conductivematerial 120 is disposed, which may be referred to as “supportingelectrode”, has an insulating property.

The conductive material 120 is preferably at least one metal selectedfrom transition metals, such as Cu, Ni, Co, Ag, Pd, Rh, Ru, Au, Pt, andIr, for example. These metals may be used alone or in a form of analloy. Furthermore, a metal oxide of these metals or a semiconductormaterial, such as SiC, for example, may be used.

The above-described metals coated with an inorganic material, such asAl₂O₃, ZrO₂, or SiO₂ or a mixed calcined material such as a BAS materialspecifically described below, for example, may be used instead of theconductive material 120. Alternatively, the above-described metalscoated with an organic material, such as a resin, for example, may beused instead of the conductive material 120. By using such coatedpowder, the contact between particles of the conductive material isprevented and the short-circuit resistance is improved.

In the ESD protection device 110, when a voltage equal to or greaterthan a certain voltage is applied between the external electrodes 122and 124, discharge is generated between the discharge electrodes 116 and118 that face each other in the cavity 113. Since the conductivematerial 120 is in contact with the top surface 114 a and the bottomsurface 114 b that define the cavity 113, electrons easily move and,thus, a discharge phenomenon can be more efficiently produced.

In other words, the discharge phenomenon that occurs between thedischarge electrodes 116 and 118 is primarily creeping discharge that isgenerated along the interface between a gas phase of the cavity 113 andthe substrate body 112, which is an insulator, that is, along an innercircumferential surface including the top surface 114 a and the bottomsurface 114 b that define the cavity 113. Creeping discharge is adischarge phenomenon in which current flows along a surface of amaterial (insulator). Although it has been described that electronsflow, it is believed that, in reality, the electrons move by hoppingalong the surface and ionizing the gas. It is also believed that thepresence of conductive powder on the surface of an insulator decreasesthe apparent distance which the electrons hop and imparts directionalityto the electrons, thereby generating creeping discharge more actively.

If discharge is efficiently generated between the discharge electrodes116 and 118, the distance between the discharge electrodes 116 and 118can be decreased. The fluctuation in responsivity to ESD caused byvariations in the distance between the discharge electrodes 116 and 118can also be reduced. Thus, stable responsivity to ESD is achieved.

Since the conductive material 120 is in contact with the top surface 114a and the bottom surface 114 b that define the cavity 113, theconductive material 120 is not detached from the substrate body 112 dueto the impact during discharge. Therefore, the ESD dischargecharacteristics are not degraded after repetitive discharges. Inaddition, since a portion of the conductive material 120 is buried ininsulating layers 112 a and 112 b of the substrate body 112 as shown inFIG. 19, detachment of the conductive material 120 is further preventedwith certainty.

Furthermore, since the conductive material 120 is in contact with boththe top surface 114 a and the bottom surface 114 b that define thecavity 113, creeping discharge is easily generated along both the topsurface 114 a and the bottom surface 114 b. Therefore, the area in whichcreeping discharge is generated is approximately doubled as compared tothe case in which a conductive material is dispersed on only the bottomsurface as in Comparative Example 2 described below. As a result,creeping discharge is more easily generated and, thus, the ESD dischargecharacteristics are further improved.

A method for manufacturing the ESD protection device 110 will now bedescribed.

First, materials for forming a substrate body 112, a cavity 113, aconductive material 120, and discharge electrodes 116 and 118 areprepared.

A ceramic green sheet for forming the substrate body 112 is prepared asfollows.

A material primarily including Ba, Al, and Si (BAS material) is used asa ceramic material. Raw materials are prepared and mixed so that themixture has a desired composition, and then calcined at about 800° C. toabout 1000° C. The calcined powder is pulverized using a zirconia ballmill for about 12 hours to obtain ceramic powder. An organic solvent,such as toluene or EKINEN, for example, is added to the BASmaterial-calcined ceramic powder and mixed. A binder and a plasticizerare further added thereto and mixed to obtain slurry. The obtainedslurry is molded on a PET film by a doctor blade method to obtain aceramic green sheet having a thickness of about 50 μm, for example.

The ceramic material is not particularly limited to the above-describedmaterial as long as the ceramic material has an insulating property.Therefore, such a ceramic material may be a mixture of forsterite andglass, a mixture of CaZrO₃ and glass, or other suitable material, forexample.

A toner for forming a supporting electrode, which is chargeable powderincluding a conductive material 120 to be disposed in the cavity 113, isprepared as follows.

1. Surface copper oxide powder having an average particle size of about14 μm, for example, and an acrylic resin are preferably mixed with eachother, and the surface of the Cu powder is covered with the resin usinga surface-treating machine.

2. The sample obtained through the process 1 is classified using aclassifier to remove fine powder and coarse powder.

3. The composite powder obtained by coating the surface of copper withthe acrylic resin through the process 2 is dispersed in an aqueoussolution in which a dispersant is dissolved. After the composite powderis precipitated, the supernatant liquid is removed and the compositepowder is dried in a vacuum drying oven.

4. The composite powder obtained through the process 3 and an externaladditive (silica powder) are mixed with each other, and the externaladditive is uniformly attached to the surface of the composite powderusing a surface-treating machine to obtain a toner for forming asupporting electrode.

The conductive material defining the toner for forming a supportingelectrode is preferably at least one metal selected from transitionmetals, such as Cu, Ni, Co, Ag, Pd, Rh, Ru, Au, Pt, and Ir, for example.These metals may be used alone or in a form of an alloy. Furthermore, ametal oxide of these metals, a semiconductor material such as SiC, or aresistive material, for example, may be used.

The average particle size of the toner for forming a supportingelectrode is preferably about 3 μm to about 30 μm, and more preferablyabout 5 μm to about 20 μm, for example. When the average particle sizeof the toner for forming a supporting electrode is about 20 μm or less,the toner can be easily dispersed so as not to cause short circuitsbetween discharge electrodes. When the average particle size of thetoner for forming a supporting electrode is about 5 μm or more, thedistance between ceramic layers that sandwich the toner for forming asupporting electrode in a vertical direction can be satisfactorilyensured, and thus, the gap between the upper and lower ceramic layers isprevented from being filled with glass during firing.

For the toner for forming a supporting electrode, the content of theconductive material is preferably about 10 wt % to about 95 wt %, andmore preferably about 30 wt % to about 70 wt %, for example. When thecontent of the conductive material is about 95 wt % or less, thedegradation of chargeability caused when the conductive material isexposed on the surface due to an insufficient amount of resin in thetoner is easily prevented. When the content of the conductive materialis about 10 wt % or more, discharge is easily and efficiently generatedby the supporting electrode.

The resin that coats the toner is preferably a resin that has goodcharging characteristics and is eliminated through combustion,decomposition, fusion, and vaporization when fired so that the surfaceof the conductive material is exposed. Examples of the resin includeacrylic resins, styrene-acrylic resins, polyolefin resins, polyesterresins, polypropylene resins, and butyral resins. Herein, the resin isnot necessarily completely eliminated, and a resin having a thickness ofabout 10 nm may remain.

A toner for forming a cavity, which is chargeable powder for forming thecavity 113, is prepared by mixing acrylic beads having an averageparticle size of about 15 μm, for example, and an external additive witheach other and then uniformly attaching the external additive to thesurface of the acrylic beads using a surface-treating machine.

The resin material defining the toner for forming a cavity is preferablyat least one resin selected from resins that are eliminated throughcombustion, such as acrylic reins, styrene-acrylic resins, polyolefinresins, polyester resins, and butyral resins and resins that aredecomposed into monomers at high temperature, for example. These resinscan be used alone or in combination.

The average particle size of the toner for forming a cavity ispreferably about 3 μm to about 30 μm, and more preferably about 5 μm toabout 20 μm, for example. When the average particle size of the tonerfor forming a cavity is about 20 μm or less, a large void is not formedafter firing even if the toner for forming a cavity is scattered onto abackground portion other than the pattern. When the average particlesize of the toner for forming a cavity is about 5 μm or more, thedistance between ceramic layers that sandwich the toner for forming asupporting electrode in a vertical direction can be satisfactorilyensured, and thus, the gap between the upper and lower ceramic layers isprevented from being filled with glass during firing.

The particle size of the toner for forming a cavity is preferably equalor substantially equal to that of the toner for forming a supportingelectrode.

The material defining the toner for forming a cavity is preferablyeliminated at a temperature less than or equal to the temperature (about600° C. to about 700° C.) at which glass in a ceramic flows. In the casein which glass flows after the toner for forming a cavity is eliminatedand a cavity is formed, the conductive material can be secured and thesurface roughness of the creepage surface can be decreased.

In contrast, when the material defining the toner for forming a cavityis eliminated at a temperature greater than or equal to the temperature(about 600° C. to about 700° C.) at which glass in a ceramic flows, thecavity is prevented from being filled with glass that oozes out from aceramic layer. In this case, for example, carbon can be used as thematerial that defines the toner for forming a cavity and is to beeliminated.

A discharge electrode paste for forming the discharge electrodes 116 and118 is prepared as follows. A sample obtained by adding a solvent toabout 80 wt % Cu powder having an average particle size of about 2 μmand a binder resin composed of ethyl cellulose or other suitable resinis stirred and mixed.

The conductive material defining the discharge electrode paste ispreferably at least one metal selected from transition metals, such asCu, Ni, Co, Ag, Pd, Rh, Ru, Au, Pt, and Ir, for example. These metalsmay be used alone or in a form of an alloy. Furthermore, a metal oxideof these metals may be used.

A conductive material is attached to the prepared ceramic green sheet byxerography.

1. The toner for forming a supporting electrode, which includes aconductive material, and the toner for forming a cavity are mixed so asto have a volume ratio of about 1:1, for example.

2. The mixed toner obtained through the process 1 is mixed with acarrier to prepare a transfer toner.

3. A photoconductor is uniformly charged.

4. The charged photoconductor is irradiated with light using an LED in apattern of a supporting electrode, to form a latent image. In theproduction example, the supporting electrode preferably had a pattern ofabout 30 μm×about 100 μm, which was substantially the same size as thatof the gap between discharge electrodes.

5. A development bias is applied to develop the transfer toner on thephotoconductor.

6. A ceramic green sheet is disposed on the photoconductor on which thepattern of the transfer toner has been developed, to transfer thetransfer toner onto the ceramic green sheet.

7. The ceramic green sheet onto which the pattern of the transfer tonerhas been transferred is inserted into an oven to fix the toner. Thus, aceramic green sheet in which the toner for forming a supportingelectrode, which includes a conductive material, and the toner forforming a cavity are disposed in a region where a cavity is to be formedis obtained.

By transferring onto the ceramic green sheet the transfer toner in whichthe toner for forming a supporting electrode, which includes aconductive material, and the toner for forming a cavity are uniformlymixed with each other, the distance between particles of conductivematerial is ensured with certainty and, thus, stable responsivity to ESDare achieved.

For the transfer toner defined by the toner for forming a supportingelectrode, which includes a conductive material, and the toner forforming a cavity, the content of the toner for forming a supportingelectrode in the transfer toner is preferably about 10% to about 90% byvolume, and more preferably about 20% to about 80% by volume, forexample. When the content of the toner for forming a supportingelectrode in the transfer toner is about 20% or more, satisfactory ESDdischarge characteristics is easily achieved due to the conductivematerial, such as a conductive powder. When the content of the toner forforming a supporting electrode in the transfer toner is about 80% orless, a sufficient size gap is formed between particles of theconductive material, such as a conductive powder, and, thus, shortcircuits between the discharge electrodes are easily prevented.

In the production example, the size of the supporting electrode patternin which the transfer toner is disposed was set to be the same orsubstantially the same as the gap between the discharge electrodes.However, the size may be increased by about 10 μm to about 50 μm tocompensate for printing displacement. Alternatively, the size of thedischarge electrode pattern may be increased by about 10 μm to 50 μmwith respect to the supporting electrode pattern in which the transfertoner is disposed.

Discharge electrodes are formed by screen printing. That is, a dischargeelectrode pattern is formed by screen printing on the surface of theceramic green sheet on which the supporting electrode pattern has beentransferred using the transfer toner. In the production example, thedischarge electrodes were formed so that the width of each of thedischarge electrodes was preferably about 100 μm, for example, and thedischarge gap between the edges of the discharge electrodes waspreferably about 30 μm, for example.

In the production example, the discharge electrode pattern was formed byscreen printing, but a publicly known wiring pattern formation methodsuch as xerography, ink jet printing, thermal transfer printing, gravureprinting, or direct-writing printing may be suitably used.

Subsequently, the ceramic green sheets are laminated and fired asfollows.

1. The discharge electrode pattern is formed on ceramic green sheets onwhich the pattern needs to be formed.

2. All the ceramic green sheets are laminated and press-bonded to form alaminated body.

3. The laminated body is cut into chips using a die in the same manneras in a chip-type component such as an LC filter. In the productionexample, the laminated body was cut into chips each preferably having asize of about 1.0 mm×about 0.5 mm, for example.

4. The electrode paste is applied to the end surfaces of each of thechips to form external electrodes.

5. Firing is performed in a N2 atmosphere. In the case in which an inertgas, such as Ar or Ne, for example, is introduced into the cavity todecrease the corresponding voltage to ESD, firing may be performed in anatmosphere of an inert gas, such as Ar or Ne, for example, in atemperature range in which a ceramic material is shrunk and sintered. Ifthe electrode material is not oxidized (e.g., Ag), the firing may beperformed in the air.

Since the resin toner for forming a cavity is eliminated during firing,the portion in which the resin toner for forming a cavity was presentbecomes hollow.

The ceramic material is shrunk during firing, thereby exerting a forcethat sandwiches the conductive material included in the toner forforming a supporting electrode in a vertical direction. As a result, theconductive material is secured more firmly.

Through the shrinking of the ceramic material during firing, the heightof the cavity is decreased to about 60% to about 80% of the height of aportion that is to be the cavity before firing. In other words, theconductive material is engaged and buried in the upper and lower ceramiclayers by a shrinkage of about 20% to about 40%, and, thus, securelyheld by the ceramic layers.

After the firing, Ni plating and Sn plating are performed on theexternal electrodes to complete an ESD protection device.

By manufacturing an ESD protection device using a ceramic substrate asdescribed above, a cavity and a conductive material sandwiched anddispersed between the top surface and the bottom surface that define thecavity is easily formed.

In the production example, a resin was used for the toner for forming acavity. However, any material, such as carbon, for example, may be usedinstead of a resin as long as the material is eliminated during firing.

The width of the region in which the conductive material 120 is disposedmay preferably be equal to or less than the width of the dischargeelectrodes. In the production example, the conductive material 120 ispreferably disposed in only a region 113 k that is sandwiched betweenthe edges 116 k and 118 k of the discharge electrodes 116 and 118, theregion 113 k being indicated by a chain line in FIG. 20. However, asshown in FIG. 20, the conductive material 120 may be disposed in andoutside the region 113 k indicated by the chain line. Alternatively, theconductive material 120 may be disposed in only a portion of the region113 k indicated by the chain line.

Comparative Example 2

An ESD protection device 110 x of a Comparative Example 2 will bedescribed with reference to FIGS. 27 and 28.

FIG. 27 is a sectional view of an ESD protection device 110 x. FIG. 28is an enlarged sectional view of a principal portion that schematicallyshows a region 111 indicated by a chain line in FIG. 27.

As shown in FIG. 27, the ESD protection device 110 x includes a cavity113 provided in a substrate body 112 x of a ceramic multilayersubstrate, such that portions 117 and 119 of discharge electrodes 116and 118 are exposed in the cavity 113 as in Example 2-1. The dischargeelectrodes 116 and 118 are respectively connected to external electrodes122 and 124 provided on a surface of the substrate body 112 x.

In the ESD protection device 110 x, unlike in Example 2-1, a supportingelectrode 114 x is arranged so as to be adjacent to a portion 115between the discharge electrodes 116 and 118. As shown in FIG. 28, thesupporting electrode 114 x is a region in which a conductive material120 x is dispersed in an insulating material defining the substrate body112 x and has an insulating property. A portion of the conductivematerial 120 x is exposed in the cavity 113. The supporting electrode114 x is formed by applying a paste for forming a supporting electrodethat includes, for example, a ceramic material and a conductive materialto a ceramic green sheet.

In the ESD protection device 110 x, a portion of the conductive material120 x in the supporting electrode 114 x is likely to be scattered due tothe impact during discharge, whereby the distribution density of theconductive material 120 x may be decreased. Therefore, the dischargevoltage is gradually increased after repetitive discharges, and the ESDdischarge characteristics are degraded.

The ESD protection devices of Comparative Example 2 and Example 2-1,whose substrate body was a ceramic multilayer substrate, weremanufactured. The discharge voltage when a voltage of about 8 kV wasrepeatedly applied was measured for 100 samples of each of ComparativeExample 2 and Example 2-1. FIG. 23 shows the measurement results.

As is clear from FIG. 23, by interposing a conductive material betweenthe insulating layers of a substrate body as in Example 2-1, thedegradation of ESD characteristics during repetitive discharges isprevented as compared to Comparative Example 2.

It is also clear that the discharge starting voltage of Example 2-1 isless than that of Comparative Example 2, and the ESD dischargecharacteristics are improved in Example 2-1 as compared to ComparativeExample 2.

Modification 2-1

As shown in FIG. 21, which is a sectional view similar to FIG. 20,conductive materials 120 a, 120 b, and 120 c having different sizes maypreferably be disposed in a cavity 113 in a mixed manner so as to besandwiched between the top surface and the bottom surface that definethe cavity 113.

Modification 2-2

As shown in FIG. 22, which is a sectional view similar to FIG. 20,conductive materials 120 s and 120 t having polygonal shapes maypreferably be disposed in a cavity 113 so as to be sandwiched betweenthe top surface and the bottom surface that define the cavity 113.

Example 2-2

An ESD protection device of an Example 2-2 of a preferred embodiment ofthe present invention will be described with reference to FIG. 24.

Example 2-2 has substantially the same configuration as Example 2-1.Hereinafter, the same elements and components as those in Example 2-1are designated by the same reference numerals, and the differencesbetween Example 2-1 and Example 2-2 will be primarily described.

A substrate body of the ESD protection device of Example 2-2 is aceramic multilayer substrate including a ceramic material and a glassmaterial. As shown in FIG. 24, glass layers 115 a and 115 b are definedby a glass material that has oozed out from the insulating layers 112 pand 112 q of a substrate body primarily made of a ceramic material intoa cavity 113 p during firing. A top surface 114 p and a bottom surface114 q that define the cavity 113 p are respectively formed of the glasslayers 115 a and 115 b.

The glass layers 115 a and 115 b can be formed so as to have a desiredthickness by adjusting the amount of the glass material that oozes outfrom the ceramic layers 112 p and 112 q, the amount being adjusted bycontrolling the atmosphere, e.g., 02 concentration and H₂ concentration,during firing. Since the ESD discharge characteristics are degraded ifthe entire conductive material 120 is covered with the glass material,the firing atmosphere is preferably adjusted so that only the upper andlower portions of the conductive material 120 are covered with the glassmaterial.

If the glass material excessively oozes out, the cavity is filled withthe glass material and the ESD discharge characteristics are degraded.Therefore, the height of the cavity is preferably about 5 μm to about 30μm.

The amount of the glass material that oozes out can also be adjusted bychanging the composition of the ceramic material defining the ceramiclayers 112 p and 112 q that sandwiches the conductive material 120.Glass may be added to the ceramic material actively.

Examples of the glass added include various glasses, such asborosilicate glass, feldspathic crystalline glass, cordierite glass,diopside glass, and lanthanoide titanate glass.

In Example 2-2, advantages equal to or better than those of Example 2-1are achieved.

That is, since the responsivity to ESD is improved due to the conductivematerial 120 in contact with the top surface 114 p and the bottomsurface 114 q that define the cavity 113 p, ESD characteristics areeasily adjusted and stabilized. Furthermore, the surface roughness ofthe top surface 114 p and the bottom surface 114 q that define thecavity 113 p is decreased because the top surface 114 p and the bottomsurface 114 q are defined by the glass layers 115 a and 115 b.Therefore, the distance which electrons move during creeping dischargeis decreased, and thus, the responsivity to ESD is further improved.

Since the conductive material 120 is in contact with both the topsurface 114 p and the bottom surface 114 q that define the cavity 113 p,the responsivity to ESD can be further improved as compared to the casein which a conductive material is dispersed on only one of the surfaces.

The conductive material 120 is fixed to the substrate body via the glasslayers 115 a and 115 b. Therefore, detachment of the conductive material120 from the substrate body is more effectively prevented as compared tothe case in which the conductive material 120 is merely in contact withthe substrate body. Consequently, the degradation of ESD characteristicscaused by repetitive discharges, e.g., an increase in discharge startingvoltage, is further prevented.

Example 2-3

An ESD protection device 110 a of an Example 2-3 of a preferredembodiment of the present invention will be described with reference toFIG. 25.

As shown in a sectional view of FIG. 25, unlike in Example 2-1,aggregates 130, 132, and 134 of a conductive material are sandwichedbetween a top surface 114 s and a bottom surface 114 t that define acavity 113 a. The aggregates 130, 132, and 134 of a conductive materialare dispersed in the cavity 113 a.

In Example 2-3, the same advantages as in Example 2-1 are achieved.

That is, since the responsivity to ESD is improved due to the aggregates130, 132, and 134 of a conductive material that are in contact with thetop surface 114 s and the bottom surface 114 t that define the cavity113 a, ESD characteristics are easily adjusted and stabilized.

Since the aggregates 130,132, and 134 of a conductive material are incontact with both the top surface 114 s and the bottom surface 114 tthat define the cavity 113 a, the responsivity to ESD is furtherimproved as compared to the case in which the a conductive material isdispersed on only one of the surfaces.

Furthermore, since the aggregates 130, 132, and 134 of a conductivematerial are in contact with both the top surface 114 s and the bottomsurface 114 t that define the cavity 113 a, the detachment of theconductive material from the substrate body 112 a is prevented.Consequently, the degradation of ESD characteristics caused byrepetitive discharges, e.g., an increase in discharge starting voltage,is prevented.

Example 2-4

An ESD protection device of an Example 2-4 of a preferred embodiment ofthe present invention will be described with reference to FIGS. 26A and26B.

An ESD protection device of Example 2-4 is different from that ofExample 2-1 in that the substrate body is made of a resin.

A method for manufacturing the ESD protection device of Example 2-4 willbe described with reference to an exploded sectional view of FIGS. 26Aand 26B.

A substrate A schematically shown in FIG. 26A is prepared. That is,discharge electrodes 116 a and 118 a are formed by stacking Cu foil on aprepreg 112 s and patterning the Cu foil through photolithography.

A substrate B schematically shown in FIG. 26B is prepared. Chargeablepowder (hereinafter referred to as “conductive material-containingtoner”) 160 that includes a conductive material is disposed on a prepreg112 t in a dispersed manner by xerography.

As indicated by an arrow 180, the substrate A, which is completelycured, is disposed on the substrate B, which is semi-cured, and they arebonded to each other through the complete cure of the substrate B. Acavity is formed between an edge 116 t of the discharge electrode 116 aand an edge 118 t of the discharge electrode 118 a by the thickness ofthe Cu foil of the substrate A. The conductive material-containing toner160 is supported while being sandwiched between the substrate A and thesubstrate B in the cavity.

Alternatively, after the substrate B is completely cured, the substrateA and the substrate B may be bonded to each other using an adhesive.

A baking electrode or a conductive resin electrode is formed on the endsurfaces of the bonded substrate, and plating is performed thereon toobtain external electrodes.

Through the processes described above, the ESD protection device iscompleted.

In Example 2-4, substantially the same advantages as in Example 2-1 areachieved.

That is, since the responsivity to ESD is improved due to the conductivematerial-containing toner 160 that is in contact with the top surfaceand the bottom surface (the substrate A and the substrate B) that definethe cavity, ESD characteristics are easily adjusted and stabilized.

Since the conductive material-containing toner 160 is in contact withboth the top surface and the bottom surface (the substrate A and thesubstrate B) that define the cavity, the responsivity to ESD is furtherimproved as compared to the case in which a conductive material isdispersed on only one of the surfaces.

Furthermore, since the conductive material-containing toner 160 is incontact with both the top surface and the bottom surface (the substrateA and the substrate B) that define the cavity, detachment of theconductive material-containing toner 160 from the substrate A and thesubstrate B is prevented. Consequently, the degradation of ESDcharacteristics caused by repetitive discharges, e.g., an increase indischarge starting voltage, is prevented.

Example 3-1

An ESD protection device 210 of an Example 3-1 of a preferred embodimentof the present invention will be described with reference to FIGS. 29 to32. FIG. 29 is a sectional view of an ESD protection device 210.

As shown in FIG. 29, the ESD protection device 210 preferably includes acavity 213 provided in a substrate body 212 of a ceramic multilayersubstrate. A pair of discharge electrodes 216 and 218 are disposed suchthat the respective edges 216 k and 218 k are exposed in the cavity 213.The discharge electrodes 216 and 218 extend to the peripheral surface ofthe substrate body 212 and are respectively connected to externalelectrodes 222 and 224 provided on the surface of the substrate body212. The external electrodes 222 and 224 are used to connect the ESDprotection device 210 to a device.

The edges 216 k and 218 k of the discharge electrodes 216 and 218 arearranged to face each other with a space provided therebetween. When avoltage equal to or greater than a certain voltage is applied from theexternal electrodes 222 and 224, discharge is generated between thedischarge electrodes 216 and 218 in the cavity 213.

A supporting electrode portion 214 indicated by a chain line ispreferably arranged along the inner surface 213 s of a region betweenthe discharge electrodes 216 and 218, the inner surface 213 s being aportion of the inner surface that define the cavity 213, and along theinterface between the substrate body 212 and the discharge electrodes216 and 218.

Specifically, as schematically shown in an enlarged sectional view of aprincipal part in FIG. 30, in the supporting electrode portion 214,conductive material powder 260 is preferably arranged in a single layersuch that only a single particle of the conductive material powder 260is provided in the thickness direction. As a result, particles of theconductive material powder 260 can be arranged with a high probabilitythat the particles are separated from each other as compared to asupporting electrode portion including particles of conductive materialpowder that are mixed and three-dimensionally dispersed as inComparative Example 3 described below. Therefore, the generation ofshort circuits between the discharge electrodes 216 and 218 is preventedand thus short-circuit resistance is improved.

As shown in FIG. 30 and a perspective view of FIG. 31, preferably, aportion of the conductive material powder 260 protrudes from the innersurface 213 s of the region between the discharge electrodes 216 and 218into the cavity 213 and another portion is buried in the substrate body212. When the conductive material powder 260 is exposed in the cavity213 from the inner surface 213 s between the discharge electrodes 216and 218, creeping discharge is further promoted and the ESDcharacteristics are improved. For example, discharge starting voltage isdecreased and the responsivity to ESD is improved.

Herein, the conductive material powder 260 may preferably be completelyburied in the substrate body 212 so as not to be exposed in the cavity213 at all.

In the supporting electrode portion 214, the conductive material powder260 only needs to be disposed at least in the region between thedischarge electrodes 216 and 218. If the supporting electrode portion214 is arranged so that the conductive material powder 260 is furtherdisposed outside the region, that is, along the interface between thesubstrate body 212 and the discharge electrodes 216 and 218, thealignment precision between the supporting electrode portion 214 and thedischarge electrodes 216 and 218 is improved as compared to the case inwhich a supporting electrode portion is arranged so that the conductivematerial powder 260 is disposed in only the region between the dischargeelectrodes 216 and 218. Consequently, the variation in dischargestarting voltage is decreased and the production cost is reduced.

The conductive material powder 260 may preferably be disposed in theregion between the discharge electrodes 216 and 218 and the regionperipheral thereto in a uniform density. Alternatively, the conductivematerial powder 260 may preferably be disposed in a non-uniform density,for example, in the form of a belt defined by a single row or aplurality of rows, a mesh, or an island, for example.

The ceramic material included in a base material of the supportingelectrode portion 214 and the ceramic material included in the substratebody 212 that is present in a portion other than the supportingelectrode portion 214 may be the same as or different from each other.However, if the ceramic materials are the same, the shrinkage behaviorof the supporting electrode portion 214 can be easily matched with thatof the substrate body 212, which decreases the number of types ofmaterials used. The conductive material powder 260 included in thesupporting electrode portion 214 may be the same as or different fromthat of the discharge electrodes 216 and 218. However, if the materialsare the same, the shrinkage behavior of the conductive material powder260 can be easily matched with that of the discharge electrodes 216 and218, which decreases the number of types of materials used.

Since the supporting electrode portion 214 includes the conductivematerial powder 260 and the ceramic material, the shrinkage behavior ofthe supporting electrode portion 214 during firing can be controlled tobe an intermediate shrinkage behavior between that of the dischargeelectrodes 216 and 218 and that of the substrate body 212. Thus, thedifference in shrinkage behavior during firing between the dischargeelectrodes 216 and 218 and the substrate body 212 can be reduced byusing the supporting electrode portion 214. As a result, failure due to,for example, detachment of the discharge electrodes 216 and 218 orcharacteristic variation is prevented. In addition, the variation incharacteristics, such as discharge starting voltage, is preventedbecause the variation in the distance between the discharge electrodes216 and 218 is prevented.

The coefficient of thermal expansion of the supporting electrode portion214 can be adjusted to an intermediate value between that of thedischarge electrodes 216 and 218 and that of the substrate body 212.Thus, the difference in a coefficient of thermal expansion between thedischarge electrodes 216 and 218 and the substrate body 212 can bereduced by using the supporting electrode portion 214. As a result,failure due to, for example, detachment of the discharge electrodes 216and 218 or the changes in characteristics over time is prevented.

By adjusting the amount and type of the conductive material powder 260included in the supporting electrode portion 214, the discharge startingvoltage can be set to a desired voltage. Thus, the discharge startingvoltage can be set with high precision as compared to the case in whicha discharge starting voltage is adjusted using only the distance betweenthe discharge electrodes 216 and 218.

A method for manufacturing the ESD protection device 210 will now bedescribed.

A material primarily including Ba, Al, and Si (BAS material) ispreferably used as a ceramic material.

Raw materials are prepared and mixed so that the mixture has a desiredcomposition, and then calcined at about 800° C. to about 1000° C. Thecalcined powder is pulverized using a zirconia ball mill for about 12hours to obtain ceramic powder. An organic solvent, such as toluene orEKINEN, for example, is added the ceramic powder and mixed. A binder anda plasticizer are further added thereto and mixed to obtain slurry. Theobtained slurry is molded by a doctor blade method to obtain a greensheet having a thickness of about 50 μm, for example.

Next, an electrode paste is prepared. A solvent is added to about 80 wt% Cu powder having an average particle size of about 2 μm, for example,and a binder resin made of ethyl cellulose or other suitable resin, andthe mixture is stirred and mixed using a three-roll mill to obtain anelectrode paste.

A resin paste including only a resin and a solvent is prepared as anelimination material by substantially the same method. A resin that iseliminated through combustion, decomposition, fusion, or vaporizationwhen fired is preferably used. Examples of the resin include PET,polypropylene, ethyl cellulose, and acrylic resin.

A supporting electrode portion is formed on a green sheet by xerographyor a transferring method.

The volume of Cu powder exposed can be set to be about 10% to about 95%,and the volume is preferably controlled to be about 20% to about 80%,for example. If the volume of Cu powder exposed is excessively small,satisfactory characteristics of discharge responsivity to ESD are notachieved. If the volume is excessively large, that is, the volume of Cupowder buried is excessively small, the Cu powder is detached from thesubstrate.

A supporting electrode portion is formed by xerography or a transferringmethod.

In the case in which the supporting electrode portion is formed byxerography, conductive material powder is processed into toner, and thesupporting electrode material is formed using the prepared toner.

Specifically, the toner is prepared as follows.

1. Cu powder having an average particle size of about 3 μm, for example,and a resin are mixed with each other, and the surface of the Cu powderis covered with the resin using a surface-treating machine.

2. The sample obtained through the process 1 is classified to removefine powder and coarse powder.

3. The capsulated Cu powder obtained through the process and an externaladditive are mixed with each other, and the external additive isuniformly attached to the surface of the capsulated Cu powder using asurface-treating machine.

4. The capsulated Cu powder obtained through the process 3 and a carrierare mixed with each other to obtain a developer.

Specifically, the supporting electrode portion is formed as follows.

1. A photoconductor is uniformly charged.

2. The charged photoconductor is irradiated with light using an LED in apattern of a supporting electrode portion, to form a latent image.

3. A development bias is applied to the photoconductor to develop thetoner on the photoconductor. The amount of the toner applied iscontrolled using the bias.

4. A ceramic green sheet is disposed on the photoconductor on which apattern of the supporting electrode portion has been developed, totransfer the toner onto the ceramic green sheet.

5. The ceramic green sheet onto which the pattern of the supportingelectrode portion has been transferred is inserted into an oven to fixthe toner. Thus, a ceramic green sheet having a pattern of a supportingelectrode portion is obtained.

6. The volume of conductive material powder exposed in the cavity, i.e.,the volume of conductive material powder buried, is controlled byadjusting the pressure applied when the ceramic green sheet is disposedon the photoconductor to transfer the toner onto the ceramic greensheet. Alternatively, the volume is controlled by adjusting the pressureapplied, using a roller or other pressure applying device, to thesurface of the ceramic green sheet onto which the toner has beentransferred.

In the case of a transferring method, the supporting electrode portionis formed as follows.

1. A photosensitive adhesive sheet is irradiated with light in a patternof a supporting electrode portion.

2. Cu powder having an average particle size of about 3 μm is providedon the photosensitive adhesive sheet so that the Cu powder is attachedin the pattern formed on the photosensitive adhesive sheet. The amountof the conductive material powder applied is controlled by dividing thepattern into a mesh.

3. The photosensitive adhesive sheet having the Cu powder disposedthereon is transferred onto the ceramic green sheet to form a pattern ofa supporting electrode portion.

4. The volume of the Cu powder exposed in the cavity is controlled byadjusting the pressure applied during transfer.

The electrode paste is applied by screen printing on the green sheetincluding the supporting electrode portion formed thereon to formdischarge electrodes having a discharge gap therebetween. Herein, thedischarge electrodes were formed so that the width of each of thedischarge electrodes was preferably about 100 μm, for example, and thedischarge gap between the discharge electrodes was preferably about 30μm, for example. The resin paste is applied thereon at a position atwhich a cavity is to be formed.

Lamination and press bonding are performed in substantially the samemanner as in a typical multilayer product. Herein, the lamination wasperformed so that the thickness was preferably set to be about 0.35 mm,for example, and the discharge electrodes and the resin pastecorresponding to a cavity were arranged in the approximate center in thethickness direction.

The laminated body is cut into chips using a die in substantially thesame manner as in a chip-type product, such as an LC filter. Herein, thelaminated body was cut into chips each having a size of about 1.0mm×about 0.5 mm, for example. After that, the electrode paste is appliedto end surfaces to form external electrodes.

Firing is performed in a N2 atmosphere in substantially the same manneras in a typical multilayer product. The resin paste is eliminated duringfiring, and thus, a cavity is formed.

In the case in which an inert gas, such as Ar or Ne, for example, isintroduced into the cavity to decrease the response voltage to ESD,firing may be performed in an atmosphere of an inert gas, such as Ar orNe, for example, in a temperature range in which a ceramic material isshrunk and sintered. If the electrode material is not oxidized (e.g.,Ag), the firing may be performed in the air.

Electrolytic Ni plating and Sn plating are performed on the externalelectrodes in substantially the same manner as in a chip-type product,such as an LC filter.

Through the processes described above, the ESD protection device iscompleted.

The ceramic material of the substrate body is not particularly limitedto the above-described material as long as the ceramic material has aninsulating property. Therefore, such a ceramic material may be a mixtureof forsterite and glass, a mixture of CaZrO₃ and glass, or othersuitable material, for example.

The electrode material of the discharge electrodes is also not limitedto Cu, and may be Ag, Pd, Pt, Al, Ni, W, or a combination thereof, forexample.

The conductive material powder used for the supporting electrode portionis preferably at least one metal selected from transition metals, suchas Cu, Ni, Co, Ag, Pd, Rh, Ru, Au, Pt, and Ir, for example. These metalsmay be used alone or in a form of an alloy. Furthermore, a metal oxideof these metals may be used. A material having low conductivity such asa semiconductor material or a resistive material can also be used as theconductive material.

As schematically shown in an enlarged sectional view of a principalportion in FIG. 32, the supporting electrode portion may preferably beformed using particles 264 each having a coating layer 262, theparticles 264 preferably being obtained by coating the surface of powder260 of such metals with an inorganic material, such as Al₂O₃, ZrO₂, orSiO₂ or a mixed calcined material, such as BAS, for example.Alternatively, particles each coated with a coating layer 262 made of anorganic material, such as a resin may be used. By using such coatedpowder, the contact between particles of the conductive material powderis prevented and the short-circuit resistance is improved.

The coating material is preferably a material that is eliminated throughcombustion, decomposition, fusion, or vaporization when fired so thatthe surface of the conductive material powder is exposed. However, thematerial is not necessarily completely eliminated, and a material havinga thickness of about 10 nm, for example, may remain.

The average particle size of the conductive material powder ispreferably in a range of about 0.05 μm to about 10 μm, and morepreferably about 0.1 μm to about 5 μm, for example. The surface area ofthe conductive material powder exposed in the cavity is increased as theparticle size is decreased, whereby discharge starting voltage isdecreased and the responsivity to ESD is improved.

Although the resin paste has been applied to form the cavity, anymaterial, such as carbon, for example, may be used instead of a resin aslong as the material is eliminated during firing. Pasting and printingare not necessarily performed. Instead, a resin film may be attached toa position at which a cavity is to be formed.

Comparative Example 3

An ESD protection device 210 x of a Comparative Example 3 will bedescribed with reference to FIGS. 35 and 36.

As shown in a sectional view of FIG. 35, the ESD protection device 210 xof Comparative Example 3 has substantially the same configuration asthat of the ESD protection device 210 of Example 3-1, except for theconfiguration of a supporting electrode portion 214 x provided near theinner surface 213 s of the cavity 213 between the discharge electrodes216 and 218.

As schematically shown in a sectional view of a principal portion inFIG. 36, in the supporting electrode portion 214 x of the ESD protectiondevice 210 x of Comparative Example 3, the conductive material powder260 is not disposed in a single layer such that only a single particleof the conductive material powder 260 is provided in the thicknessdirection, and is mixed in the base material and three-dimensionallydisposed in a dispersed manner.

The ESD protection devices of Comparative Example 3 and Example 3-1 weremanufactured and compared to each other.

Specifically, 100 samples having different ratios (Cu ratios) of thearea of conductive material powder (Cu), of the supporting electrodeportion, exposed in the cavity relative to the area of the supportingelectrode portion were produced for each of Comparative Example 3 andExample 3-1. Short circuits between discharge electrodes and thedischarge responsivity to ESD were evaluated.

The discharge responsivity to ESD was measured using an electrostaticdischarge immunity test provided in IEC61000-4-2, which is the standardof IEC. When a voltage of about 2 kV to about 8 kV was applied throughcontact discharge, whether discharge was generated between the dischargeelectrodes of the samples was measured.

Table 2 shows the results.

TABLE 2 Parentage of Discharge responsivity to ESD Cu ratio shortcircuits 2 kV 4 kV 6 kV 8 kV C.E. A 20%  0% — — — D C.E. B 35% 10% — — DD C.E. C 50% 20% — D D D C.E. D 65% 30% D D D D Ex. 1 65%  0% D D D DC.E.: Comparative Example Ex.: Example

Herein, Cu ratio=(area of Cu powder exposed in cavity)/(area ofsupporting electrode portion).

As is clear from Table 2, by providing the structure of Example 3-1including the supporting electrode portion in which the conductivematerial powder is disposed in a single layer such that only a singleparticle of the conductive material powder is provided in the thicknessdirection, the discharge responsivity to ESD equal to or better thanthat of Comparative Example 3 including the supporting electrode portionin which the conductive material powder is disposed in a mixedarrangement is achieved while the short-circuit resistance is improved.

As described above, by using a supporting electrode portion including astructure in which conductive material powder is disposed in a singlelayer such that only a single particle of the conductive material powderis provided in the thickness direction, discharge starting voltage canbe set with high precision. As a result, a probability that particles ofconductive material powder contact each other is decreased and, thus,the short-circuit resistance is improved. By exposing a portion of theconductive material powder in the cavity so as to increase the surfacearea of the conductive material powder exposed in the cavity, adischarge phenomenon is further promoted, which further decreases thedischarge starting voltage and improves the responsivity to ESD.

Example 3-2

An ESD protection device 210 a of an Example 3-2 of a preferredembodiment of the present invention will be described with reference toFIG. 33.

FIG. 33 is a sectional view of an ESD protection device 210 a of Example3-2. As shown in FIG. 33, the ESD protection device 210 a of Example 3-2has substantially the same configuration as that of the ESD protectiondevice 210 of Example 3-1.

That is, a cavity 213 a is provided inside a substrate body 212 a andthe edges 216 t and 218 t of a pair of discharge electrodes 216 a and218 a arranged to face each other are exposed in the cavity 213 a. Thedischarge electrodes 216 a and 218 a are respectively connected toexternal electrodes 222 and 224 provided on a surface of the substratebody 212 a. In a supporting electrode portion 214 a, conductive materialpowder 260 is preferably disposed along the inner surface 213 t of thecavity 213 a between the discharge electrodes 216 a and 218 a and alongthe interface between the discharge electrodes 216 a and 218 a and thesubstrate body 212 a, the conductive material powder 260 being disposedin a single layer such that only a single particle of the conductivematerial powder 260 is provided in the thickness direction.

The ESD protection device 210 a of Example 3-2 is substantially the sameas the ESD protection device 210 of Example 3-1, except that thesubstrate body 212 a is not made of a ceramic material, and instead, ismade of a resin material.

A method for manufacturing the ESD protection device 210 a of Example3-2 will now be described with reference to an exploded sectional viewof FIGS. 34A and 34B.

A substrate A shown in FIG. 34A is prepared. That is, dischargeelectrodes 216 a and 218 a are formed by stacking Cu foil on a prepreg212 s and patterning the Cu foil through photolithography.

A substrate B shown in FIG. 34B is prepared. A supporting electrodeportion 214 a is formed by disposing conductive material powder 260(e.g., Cu powder) on a prepreg 212 t, the conductive material powder 260being disposed in a single layer such that only a single particle of theconductive material powder 260 is provided in the thickness direction.The conductive material powder 260 is disposed by the same orsubstantially the same method as in Example 3-1, such as xerography or atransferring method.

The substrate A, which is completely cured, is disposed on the substrateB, which is semi-cured body, and they are bonded to each other throughthe complete cure of the substrate B. A cavity 213 a is formed by thethickness of the Cu foil of the substrate A. Alternatively, after thesubstrate B is completely cured, the substrate A and the substrate B maybe bonded to each other using an adhesive.

A baked electrode or a conductive resin electrode is formed on the endsurfaces of the bonded substrate, and plating is performed thereon toobtain external electrodes.

Through the processes described above, the ESD protection device 210 ais completed.

In Example 3-2, substantially the same advantages as in Example 3-1 areachieved. In other words, by providing a structure in which conductivematerial powder is disposed in a single layer such that only a singleparticle of the conductive material powder is provided in the thicknessdirection, a probability that particles of conductive material powdercontact each other is decreased and, thus, the short-circuit resistanceis improved. By exposing portion of the conductive material powder inthe cavity so as to increase the surface area of the conductive materialpowder exposed in the cavity, a discharge phenomenon is furtherpromoted, which further decreases the discharge starting voltage andimproves the responsivity to ESD.

As described above, supporting electrode particles including asupporting electrode material having conductivity are dispersed in acavity provided inside a substrate body, whereby the dischargeresponsivity to ESD is improved. The fluctuation in responsivity to ESDcaused by variation in the distance between discharge electrodes isreduced. Therefore, the ESD characteristics can be easily adjusted andstabilized.

By providing a structure in which a conductive material is sandwichedbetween a top surface and a bottom surface that define a cavity, ESDcharacteristics are easily adjusted and stabilized and, thus, thedegradation of discharge characteristics caused by repetitive dischargesis prevented.

By providing a supporting electrode portion in which conductive materialpowder is disposed in a single layer such that only a single particle ofthe conductive material powder is provided in the thickness direction,the discharge starting voltage can be set with high precision and, thus,an ESD protection device with high reliability can be manufactured.

The present invention is not limited to the above-described preferredembodiments, and various modifications can be made.

For example, the substrate body may be an insulating substrate made ofan insulating material other than a ceramic or resin material.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

What is claimed is:
 1. A method for manufacturing an electrostaticdischarge (ESD) protection device comprising: a first step of forming asupporting electrode portion by disposing conductive material powder ina single layer such that only a single particle of the conductivematerial powder is provided in a thickness direction, the conductivematerial powder being disposed on a principal surface of a firstinsulating layer; a second step of forming at least one pair ofdischarge electrodes on the principal surface of the first insulatinglayer so that at least one portion of the supporting electrode portionis exposed between the at least one pair of discharge electrodes; athird step of forming a second insulating layer on the principal surfaceof the first insulating layer so that the second insulating layer coatsthe at least one pair of discharge electrodes and covers an exposedregion at which the at least one portion of the supporting electrodeportion is exposed between the at least one pair of dischargeelectrodes, the second insulating layer being separated from the exposedregion; and a fourth step of forming external electrodes on a surface ofa laminated body obtained through the third step such that the externalelectrodes are connected to the at least one pair of dischargeelectrodes; wherein a cavity surrounded by the second insulating layer,the as least one pair of discharge electrodes, and the exposed region isformed.
 2. The method for manufacturing an electrostatic discharge (ESD)protection device according to claim 1, wherein in the second step, acavity-forming layer including an elimination material is formed on atleast a portion of the supporting electrode portion that is to beexposed between the at least one pair of discharge electrodes; and afterthe second insulating layer is formed on the cavity-forming layer in thethird step, the cavity is formed by eliminating at least a portion ofthe cavity-forming layer including the elimination material.
 3. Themethod for manufacturing an electrostatic discharge (ESD) protectiondevice according to claim 1, wherein, in the first step, the supportingelectrode portion is formed by transferring, onto the first insulatinglayer, conductive material powder disposed in a single layer such thatonly a single particle of the conductive material powder is provided ina thickness direction.
 4. The method for manufacturing an electrostaticdischarge (ESD) protection device according to claim 1, wherein, in thefirst step, the supporting electrode portion is formed by xerography. 5.The method for manufacturing an electrostatic discharge (ESD) protectiondevice according to claim 1, wherein, in the first step, the conductivematerial powder, of the supporting electrode portion, disposed on theprincipal surface of the first insulating layer and in a single layersuch that only a single particle of the conductive material powder isprovided in a thickness direction, is coated with an eliminationmaterial.